The isolation last week of a "lone" quark, a sub-atomic particle that scientists previously believed could not be isolated, sent shock waves through the typically placid world of particle physics.

Physicists at Harvard and the Massachusetts Institute of Technology contacted yesterday said they are still uncertain about the implications of the discovery. William B. Fairbanks, professor of Physics at Stanfor University, who headed the experimental group that isolated the quark, presented his findings to the American Physical Society at a conference in Washington, D.C., Tuesday.

Validity Test

Dr. Sheldon Glashow, professor of Physics, said yesterday that if Fairbanks's claim is true, then "it is the biggest thing in particle physics in the last 65 years." But he said other scientists must reproduce the Stanford experiment before its validity can established.

Subterfuge

Murray Gellmann and George Zweig, two American physicists, hypothesized separately in 1964 that quarks are matter's most basic building blocks. According to their theories, protons and neutrons which form atoms are composed of triads of even smaller particles known as quarks which carry fractional electrical charges.

Scientists previously believed that quarks were analogous to the south and north poles of a magnet which cannot be isolated, even is the magnet is split into infinitesimal pieces, Alvaro DeRujula assistant professor of Physics said yesterday.

Awaiting Confirmation

If the Stanford discovery is confirmed it will have profound implications on particle physics. All the old theories about subatomic forces will be discarded, and a new theory about these interactions will have to be formulated, DeRujula said, adding that "it will be the biggest thing since the discovery of the electron."

Not Separate

Arthur Kerman, director of the center for theoretical Physics at M.I.T. said yesterday Fairbanks's findings, when tested, may show that quarks are very stable. One important implication of the stability would be that quarks can combine to form atoms with previously unknown characteristics.

Fairbanks was unavailable for comment yesterday.