Two Princeton professors won the Nobel Prize in physics yesterday for their work on pulsars, and two other researchers won the Nobel Prize in chemistry for developing techniques to manipulate DNA.

Princeton professors Russell A. Hulse, 42, and Joseph H. Taylor Jr., 52, won the prize in physics for their discovery of the first binary pulsar in 1974.

Pulsars are dying stars that emit regular bursts of light that can be detected with radio telescopes. The Taylor-Hulse pulsar system consists of two pulsars orbiting each other, and provides a highly accurate way to test Einstein's general theory of relativity.

Taylor received a Ph.D. in astronomy from Harvard University in 1968, and he taught Hulse at the University of Massachusetts at Amherst, where they made their landmark discovery nearly 20 years ago.

Kary B. Mullis, a consultant from San Diego, and Michael Smith of the University of British Columbia in Vancouver shared the prize in chemistry for inventing techniques now widely used in medical research and drug development.

Mullis, 48, invented the polymerase chain reaction (PCR) in 1983, which allows scientists to mass produce millions of copies of short sequences of DNA within a couple of hours.

Smith, 61, invented a technique called site-directed mutagenesis, which allows scientists to alter protein structure by editing genetic code.

Each pair of prizewinners will split a prize of $825,000.

Harvard professors were quick to laud the accomplishments of the new Nobel laureates.

Bernard N. Fields, professor of microbiology and molecular genetics at the Harvard Medical School, said Mullis' PCR has opened up new avenues in research, fundamental technology, and clinical medicine.

"There's no question that the method of PCR is an extremely powerful one," said Fields.

Mullis' personality may have been the only obstacle between him and a Nobel Prize. He was the subject of a profile in last Sunday's Parade magazine, which reported that he once "had a midnight brawl on a beach with a fellow researcher," and which discussed his penchant for sunning himself on the roof rather than working in lab.

Fields said Smith's technique of genetic editing was also powerful in medical research.

"Instead of having to depend on nature for isolating mutants, site directed mutagenesis gives us the power of creating mutants that we want," said Fields. "You can take certain regions of DNA and change every single base, almost at will."

According to a statement yesterday, observations of the spiraling behavior of the pulsars have come within 0.5 percent of Einstein's predictions.

The timing of the pulsars' emissions also prove for the first time the existence of gravitational waves.

"People go up against Einstein's general theory almost every day in an effort to prove it right or wrong, but the number of really accurate tests is small," said John P. Huchra, professor of astronomy and associate director of the Harvard observatory.

Huchra said he was glad that the prize was awarded for astronomy research.

"It used to be the case that no one in astronomy or astrophysics won," said Huchra. "There was a bit of prejudice against the field."

Most Harvard professors were not surprised at the winners.

"Mullis was due for a prize," said Fields. "There's no question that PCR methodology is powerful."

"I'm not surprised that someone like Joseph [Taylor] won, because he's a pretty sharp cookie," said Huchra.

Sheldon L. Glashow, professor of physics and a Nobel laureate, agreed, saying, "[Taylor and Hulse] were on my list of likelies."

So what does it feel like to win the Nobel prize?

In a statement yesterday, Taylor said, "One doesn't expect this. You occasionally hear bits and snatches of rumors, but it comes as a surprise. It's certainly a great personal honor and a reflection on the research group."

"It feels good, what can I say?" said Glashow, who won the physics Nobel in 1979. "It's a great joy to be appreciated in that fashion and to have a marvelous fairy tale trip to meet the king and queen."

The Nobel peace prize will be awarded Friday in Oslo, Norway.