Two American scientists and a Canadian won the Nobel prize for physics yesterday for proving an atom is made up not only of electrons, protons and neutrons, but of still smaller subatomic particles called quarks, the basic building blocks of the universe.

The Nobel prize for chemistry went to Harvard University researcher Elias James Corey, 62, who developed an ingenious approach to synthesizing complicated molecules that has revolutionized the development of new drugs.

"The accomplishments that he and other synthetic chemists have made in creating new molecules . . . are astounding and have to be compared with the magnificent achievements of composers like Bach, Beethoven, and Mozart," said Dudley Herschbach, a 1986 Nobel laureate in chemistry and a colleague of Corey's at Harvard.

The physics prize was awarded to Canadian Richard Taylor, 60, of Stanford University and Americans Jerome Friedman, 60, and Henry Kendall, 63, both of the Massachusetts Institute of Technology. As young men, the three began a series of experiments in the mid-1960s that rival researchers predicted would go nowhere.

But by 1973 the experiments, in which a beam of high-energy electrons were fired down a two-mile tunnel and into a pool of liquid hydrogen, had proved that quarks exist and that the universe is built entirely of these elusive entities and their indivisible partners, electrons.

"When we started, people thought it was a dead-end research project," Friedman said yesterday. "But it was so exciting. We were all very young. We were given this wonderful machine. And they said, 'Here, take this wonderful machine and do something great with it.' "

"It was a beautiful experiment, one that made people believe that quarks were real physical beasts and not a mathematical convenience," said Burton Richter, the Nobel prize-winning director of the Stanford Linear Accelerator Center (SLAC) in Palo Alto, Calif., the site of the experiments.

The chemistry prize was awarded to Corey for his pioneering work in what is known as synthetic organic chemistry, a field so central to modern biochemistry that it has been the subject of seven previous Nobel prizes.

Synthetic chemistry is concerned with the problem of how to manufacture drugs. For example, a pharmaceutical company might come upon a natural chemical found in a plant that shows promise as a heart drug. Because simply growing the plant and extracting the chemical is either impractical or uneconomical, scientists would then attempt to identify the precise molecular structure of the substance and create a copy of it in the laboratory.

But this process, known as organic synthesis, is often difficult. Each molecule is made up of some combination of tightly bound atoms. In some cases, that pattern involves thousands of atoms in an extraordinarily intricate arrangement.

Deciphering these complex molecular combinations and finding ways to reconstruct them demands equal parts of intuition and doggedness, requiring a sensibility most often compared to that of an architect or an artist.

In a research career that has spanned three decades, Corey proved to be a master at this art.

Corey's chief contribution lay in a novel approach to drug creation known as retrosynthetic analysis. Traditionally, chemists have tried to duplicate molecules by looking for similar, simpler molecules and using them as patterns to construct something as close to the desired compound as possible.

Corey argued that such thinking was backwards. He proved that chemists could be far more successful at synthesizing complicated compounds if they started with the desired compound and then figured out how to break it down to its component parts.

"He started at the top of Mount Everest and started walking down," said Jeremy Knowles, a Harvard chemistry professor and colleague of Corey's. "By the time he reached the bottom, he knew he had a route back up the mountain."

Corey was one of the first to incorporate the use of computers to construct molecules, writing programs that have enjoyed wide use in drug company laboratories. He also has produced more than 100 important chemicals, including the class of pharmaceutical compounds known as prostaglandins.

"This award has been expected for a long time," said Harvard researcher Konrad Bloch, himself a Nobel laureate in 1962. "It was not a question of whether but when."

The winning physicists were described yesterday by the former director of SLAC, Wolfgang Panovsky, as "an unusual combination of unusual people with unusual talents."

According to assorted colleagues, Taylor is the "experimentalist's experimentalist who leaves nothing to chance." He is "tall, noisy, flamboyant, loud." Kendall, a Yankee patrician and amateur mountain-climber, was described as a "superb electronics genius." He is also a founder of the Union of Concerned Scientists, an activist group critical of the nuclear power industry and space-based weapons and concerned, as Kendall put it, with "the dark side of science and technology." And Friedman? "He's solid, big, round, determined, reasonable and very brilliant," said a colleague.

Since performing their award-winning research, the three have continued to collaborate on studies of subatomic particles.

Until the experiments by Taylor, Kendall and Friedman, most physicists doubted the existence of quarks, which had been proposed by Nobel laureate Murray Gell-Mann of the California Institute of Technology. Gell-Man named his theoretical particles "quarks" after a line of doggerel in James Joyce's novel "Finnegans Wake."

Physicists yesterday compared the prize-winning experiments to classic work done early in this century by Ernest Rutherford. At the time, atoms were thought to be soft, jelly-like spheres of positive and negative charges. But Rutherford showed there was a "hard grain," the nucleus, at the atom's center. Later work showed that nuclei are made of protons and neutrons.

In the 1950s and 1960s, physicists began to suspect that protons and neutrons might be made of even smaller particles. But there appeared to be a confusing riot of candidates. And there is nothing physicists hate more than a mess. So they designed experiments that attempted to reduce the confusion to order and simplicity.

In the late 1960s, Taylor, Kendall and Friedman began shooting electrons down a tunnel and smashing them into the protons contained in the nuclei of liquid hydrogen. At high energies, the scientists began noticing that protons, like grapes, seemed to harbor hard, tiny "seeds" inside. An incoming electron would smack a seed and in the process lose energy and momentum, which could be measured. These seeds turned out to be quarks.

"The experiments were a big surprise, not just to us but to everybody," Kendall said.

The Nobel prizes are awarded by the Royal Swedish Academy of Sciences. The three physicists will share $700,000. Corey will also receive $700,000.