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.