EW inventions are immune from claims and counterclaims of precedence. Thomas Edison was embroiled in a number of patent disputes. It took years for the Wright brothers to secure their rightful claim to aircraft-powered flight.

Now a dispute is churning around credit for a modern scientific breakthrough: packet switching, the technology that breaks all data that travels over the Internet into discrete bundles that are then sent along various paths around the network and reassembled at their destination.

Aside from computer scientists, few people had heard of packet switching, much less its 1960's origins, until the 1990's. Then the Internet moved from academia into the home and the office, and histories of its development began to appear.

It was about that time that Leonard Kleinrock, a computer scientist at the University of California at Los Angeles, began to stake his claim to having been the father of packet switching. In 1996 he set up a Web page on the university's site that describes him as the "Inventor of the Internet Technology" and credits him with "having created the basic principles of packet switching."

Until Dr. Kleinrock began making his case prominently, two others - Donald Davies, a British expert on computer security, and Paul Baran, formerly of the RAND Corporation - were widely recognized as packet switching's inventors. In the early 1960's, Mr. Baran outlined a packet- switched network that would make communications less vulnerable to attack or disruption. Dr. Davies, who first applied the word "packet" to data communication in the mid-1960's, later built a small packet- switched network.

Still, some found Dr. Kleinrock's claim persuasive, if belated. This year, for example, he was among four laureates who shared a $500,000 prize for their roles in creating the Internet. The prize, administered by the National Academy of Engineering, cited Dr. Kleinrock for publishing on packet switching as early as 1961.

But Dr. Davies has struck back, in a paper published a year after his death at age 75. "In Leonard Kleinrock's work," he wrote, "I can find no evidence that he understood the principles of packet switching."

The assertion has riven the ranks of Internet pioneers. It has also left the two sides in the awkward position of arguing over an eminent colleague's final testament.

"The Internet is really the work of a thousand people," Mr. Baran said. "And of all the stories about what different people have done, all the pieces fit together. It's just this one little case that seems to be an aberration."

The dispute is all the more remarkable, those who knew Dr. Davies say, because he was known for being humble - to a fault, some say - about his own accomplishments. In addition to his work on computer networks, he was a computer security expert, working with a small development team headed by Alan Turing, the British mathematician and cryptography expert who broke German codes during World War II.

"Donald Davies is one of those men who brings to mind Harry Truman's observation that `you can accomplish anything you want in life provided you don't mind who gets the credit,' " wrote John Naughton, author of "A Brief History of the Future: From Radio Days to Internet Years in a Lifetime" (Overlook Press, 2000). Mr. Naughton's history and others like it (including one published in 1996 by this reporter) credited Dr. Davies and Mr. Baran with having invented packet switching.

Dr. Davies's last word on the subject came in a paper published posthumously last summer in The Computer Journal, a publication of the British Computer Society. However self-effacing by nature, Dr. Davies was blunt in rejecting Dr. Kleinrock's claim, though the issue may require splitting the finest of technical hairs.

For years Dr. Kleinrock was known for his work in queuing theory, a branch of mathematics that studies how long people and things spend waiting in lines, how long the lines get and how to design systems to reduce waiting. Dr. Kleinrock said in an interview that although the two fields are different, "it turns out that queuing theory is the perfect tool for analyzing the way packet networks behave."

In his paper, Dr. Davies found fault with Dr. Kleinrock for not describing message switching beyond a single node, or queue, in his 1962 doctoral thesis. "Following through such a scheme would have made an interesting study," Dr. Davies wrote. "But Kleinrock does not go beyond the single queue."

Dr. Kleinrock disputes that assertion. "My entire dissertation is devoted to data networks which consist of connected sets of single nodes," he said.

And more generally, Dr. Kleinrock called the Davies article "shocking." He and Dr. Davies had exchanged cordial e-mail in the months leading to Dr. Davies's death, Dr. Kleinrock said, and he had no idea that Dr. Davies was writing the paper.

Dr. Davies was adamant that the paper not be published until after his death, said Michael Davies, his son. "He felt that if it came out during the latter stages of his illness, he wouldn't have the strength to get in a debate about it," Mr. Davies said. "But he felt deeply that he had to set the record straight."

Yet perhaps counter to Dr. Davies's intentions, instead of helping resolve the matter, his paper has simply helped galvanize each side.

Lawrence G. Roberts, who in the late 1960's designed the Arpanet, the precursor to the Internet, has been a prominent backer of Dr. Kleinrock's claim, at least in recent years. His honors include two that were shared with Dr. Kleinrock - the National Academy of Engineering award and last year's I.E.E.E. Internet Award from the Institute of Electrical and Electronics Engineers. (The latter award, unlike the academy's prize, also recognized Dr. Davies and Mr. Baran.)

While they were graduate students and researchers at the Massachusetts Institute of Technology in the 1960's, Dr. Kleinrock became a close colleague and friend of Dr. Roberts. Inveterate casino gamblers, the two scientists together tried to beat the odds at blackjack and roulette with various clever methods. They remain good friends.

Throughout the early 1990's, when asked, Dr. Roberts pointed to his own work, as well as the work of Mr. Baran and Dr. Davies, as the major influences on his thinking when he designed the network. It wasn't until Dr. Kleinrock began to lobby for recognition that Dr. Roberts changed his mind and not only began citing Dr. Kleinrock's work but also took up his friend's cause.

In an interview, Dr. Roberts said he erred when the topic of Internet history first arose in the early 1990's. After thinking more about it, he said, he decided that Dr. Kleinrock did indeed influence his thinking when he designed the Arpanet.

"I didn't differentiate Kleinrock heavily until it got to be an issue," Dr. Roberts said. "I realized I had left out what he had contributed to what I was doing. All of us started realizing we were part of history, and we had to make it clear."

Now, if either man sees Dr. Kleinrock omitted from a citation, each is quick to correct the record.

For his part, Dr. Kleinrock acknowledges waiting until 1996 - and says he did so then only because he saw his contribution eclipsed by the claims of others.

"You might find it hard to believe, but I tend to be a modest person," he said. "I become less modest when I see people taking away the things I had done."

Even without the claim to packet switching, Dr. Kleinrock's roster of achievements - listed on his home page at www.lk.cs .ucla.edu - is impressive. In 1969 his lab at U.C.L.A. became the first node on the Arpanet and the official center for network performance testing.

An entrepreneur, Dr. Kleinrock was a co- founder of Linkabit, an early computer consulting company, in 1968. He is also founder of Nomadix, a three-year-old computer networking company in Westlake Village, Calif.

Dr. Kleinrock said the controversy had put him in an uncomfortable position. "I don't like this role of having to defend the things I've done," he said. "It's more than pride of ownership. If no one had tried to claim it, it would be different. But if someone tries to take something away, that's a proactive move, and that requires a response. It's not peaceful coexistence. History should get it right."

At the same time, Dr. Kleinrock said he believed that Dr. Davies and Mr. Baran deserved credit "on a number of fronts" - Dr. Davies for coining the term "packet" and for building his experimental network. Both should be credited with coming up with the idea of slicing messages into discrete packets, albeit after he did, Dr. Kleinrock said.

Dr. Roberts, who is now chairman and chief technology officer of Caspian Networks of San Jose, Calif., a company building a new generation of Internet switching equipment, said the appearance of the paper diminished his respect for Dr. Davies.

"He was a brilliant man," Dr. Roberts said. "I just thought he was an immense figure, and this cuts my opinion some, because he knows that this is not the truth."

Dr. Roberts was particularly surprised that Dr. Davies chose to focus on one small aspect of the technology - the dividing of messages into small pieces of equal size and sending them to several intermediate nodes on the way to their final destination.

"The question of who invented which piece may be very hard to track down, but there's a lot more to packet switching besides this little teeny piece," Dr. Roberts said. "We can argue about it, but my contention is we all were thinking about it."

But another of the Internet pioneers, Mr. Baran, a Davies ally, said he thought Dr. Davies had made a professional effort to be fair.

Mr. Baran said he exchanged extensive e- mail with Dr. Davies about Dr. Kleinrock's work in the months preceding Dr. Davies's death, though he knew nothing of the Davies paper until Dr. Davies sent him a draft early last year.

"Davies was a very gentle guy," Mr. Baran said. "What he wanted to do was make absolutely sure he really understood what Kleinrock was saying. He really bent over backwards to make sure he wasn't misinterpreting anything Kleinrock wrote."

And for every supporter of Dr. Kleinrock there is an equally opinionated detractor. Dr. Willis Ware, a scientist at the RAND Corporation who was Mr. Baran's boss there in the early 1960's, shares Dr. Davies's skepticism of Dr. Kleinrock.

He and others suggested that Dr. Davies was moved to write the paper as a point of honor. "It was clear from his paper that Davies believed that Kleinrock was stretching the truth in a way that didn't seem appropriate," Dr. Ware said.

Honor is not to be underestimated in the world of scientific achievement. "Honor is an important part of the reward system, because other rewards flow from that," said Dr. Charles Bazerman, a professor of education at the University of California at Santa Barbara and an expert on Thomas Edison. "So priority becomes a crucial issue, because it's the most basic reward."