WASHINGTON -- Two French researchers were awarded a Nobel Prize yesterday for discovering the AIDS virus, bypassing an American researcher who played a key role in the discovery.

Dr. Luc Montagnier of the World Foundation for AIDS Research and Prevention and Francoise Barre-Sinoussi of the Pasteur Institute, both in Paris, were awarded the Nobel Prize in Physiology and Medicine by the Karolinska Institute in Stockholm for their 1983 identification of what was later named the human immunodeficiency virus, or HIV.

The pair split the $1.4 million prize with Dr. Harald zur Hausen of the University of Heidelberg in Germany, who discovered that another virus, the human papilloma virus (HPV), causes cervical cancer.

Excluded from the prize was Dr. Robert C. Gallo, who for years was locked in a bitter dispute with Dr. Montagnier over credit for the discovery of HIV from work he did while at the National Cancer Institute. Dr. Gallo is now at the University of Maryland.

Although the prize's rules limit the number of scientists who can win the award to three, Jans Jornvall, scientific secretary to the assembly, made clear that the committee felt that Drs. Montagnier and Barre-Sinoussi deserved sole credit because, in 1983, they published the first papers identifying the virus in the journal Science.

Mr. Jornvall praised Dr. Gallo's work, but said the committee based its decision on the French researchers' publishing their work first.

Other researchers said Drs. Montagnier and Barre-Sinoussi clearly deserved the prize, but that it was disappointing that Dr. Gallo was excluded.

"Gallo deserves enormous credit," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. "It's a shame you can't give it to four people, because Gallo's contributions were enormous."

In a written statement, Dr. Gallo congratulated the winners, adding that he was "gratified" by Dr. Montagnier's "kind statement" that he was "equally deserving." His statement added: "I am pleased that the Nobel Committee chose to recognize the importance of AIDS with these awards, and I am proud that my colleagues and I continue to search for an AIDS vaccine."

Drs. Montagnier and Gallo were locked in a bitter dispute in the 1980s over the discovery of the virus. Beyond who should get the credit, millions of dollars were also at stake from fees for blood tests. President Ronald Reagan and French Prime Minister Jacques Chirac eventually signed an agreement in 1987 that divided the royalties equally, and Drs. Gallo and Montagnier published a paper together in The New England Journal of Medicine in 2003 acknowledging each other's work.

Dr. Fauci noted that Dr. Gallo subsequently published work that definitively established HIV as the cause of AIDS.

In announcing the award, the Nobel committee said Drs. Montagnier's and Barre-Sinoussi's initial discovery led to a series of crucial advances, including deciphering how the virus reproduces and infects cells and the development of the blood test and powerful antiviral drugs that have helped contain the spread of the virus and reduce the death toll.

Drs. Montagnier, 76, and Barre-Sinoussi, 61, could not be reached for comment, but both said they were pleased in interviews posted on the Nobel committee's Web site.

The committee also praised Dr. zur Hausen's work, saying he "went against current dogma" when he proposed that HPV caused cervical cancer, the second-most-common cancer among women and the most common sexually transmitted agent. Among other things, the work led to development of vaccines against strains of the virus.

"I'm, of course, totally surprised. It's, of course, a great pleasure for me," Dr. zur Hausen, 72, said in an interview posted on the Nobel committee's Web site.