Two American researchers and a Canadian whose detection of the tiniest known subatomic particles - "quarks" - led to an explosion of understanding of the fundamental structure of matter were honored Wednesday with the Nobel Prize in Physics.

In a late development, the 1990 Nobel Prize in Chemistry was awarded Wednesday to Elias James Corey of Harvard University for his development of the theory and methodology of organic synthesis.Jerome I. Friedman and Henry W. Kendall of the Massachusetts Institute of Technology and Canadian Richard E. Taylor of Stanford University will share a $700,000 prize. They were cited for research more than 20 years ago that has proven essential to the development of the quark model of particle physics.

Friedman and Kendall were the sixth and seventh Americans to win 1990 Nobel prizes, with Corey being the eighth. Friedman and Kendall were the 54th and 55th Americans to win the physics prize since it was first awarded in 1901. Taylor was the first Canadian. The physics prize has been awarded to a total of 137 laureates.

The Royal Swedish Academy of Science said the three physics winners were "key persons in a research team which, in a series of investigations, found clear signs that there exists an inner structure in the protons and neutrons of the atomic nucleus."

"Their discoveries are a breakthrough in our understanding of the structure of matter," the academy said in its award citation.

"I'm totally overwhelmed, surprised and very honored - all those types of things," Friedman said by telephone from a hotel in Fort Worth, Texas, where he was attending a scientific symposium. "I never really thought of that as a real possibility."

Friedman, 60, a professor of physics at MIT, said he heard the news from his wife, who received the call at their Brookline, Mass., home and then called him.

"It's starting to sink in. I awoke and I couldn't believe it. I was sort of in a semi-haze. It's very exciting," he said.

Kendall, 64, said in a telephone interview from Cambridge, Mass., that he was "overwhelmed" and had not expected to win.

Friedman said the award was for a series of experiments the three conducted at Stanford beginning in 1967 that provided the first physical evidence of the existence of fundamental particles called quarks. Previously, such particles had only been theorized to exist.

"A model had been proposed, but nobody took it seriously until one got physical evidence for it. We did the experiments that provided the first physical evidence. From that, people took the quark model seriously," he said.

"You take electrons and scatter them and observe how they scatter from the proton. Looking at the scattered particles, we saw very tiny nuggets," he said.

Quarks are subatomic particles that make up the protons and neutrons that, with electrons, form all matter. The original quark theory postulated there were three types of quarks.

Corey was honored with the chemistry prize, worth $700,000, for his "important contributions to synthetic organic chemistry."

"He has developed theories and methods that have made it possible to produce a large variety of biologically highly active complicated natural products," the academy said in its award citation.

The awarding of the chemistry prize completes the cycle of 1990 Nobel prize announcements.