While a wide gap typically separates undergraduates from Harvard's star-studded faculty, a fortunate few this fall have found a luminary in their midst.

In possibly his final year at Harvard, Nobel laureate and Lawrence Professor of Chemistry William N. Lipscomb Jr. is teaching Science A-25 "Chemistry of the 20th Century," but only for three students.

The Core course, offered at Harvard since at least the early 1960s, was "inadvertantly omitted from the [1989-90 course] catalog," said Core Program director Susan W. Lewis.

The mishap arose from a miscommunication over Lipscomb's planned retirement next year after 30 years at Harvard, she said. Core officials believed the professor retired last June, she said.

Students in the course, who learned of it through newspaper advertisements, say six have joined the course, but the Registrar's Office said Friday official enrollment stands at half that.

In any case, the students meet with Lipscomb three times a week in Mallinckrodt Laboratory's largest classroom, which seats at least 100 people.

While at least two of this fall's other Science A classes are full or overcrowded, it is unclear whether A-25's omission is responsible.

"Why 300 tried to section, I don't know," said Professor of Astronomy and the History of Science Owen Gingerich.

Lead professor for Science A-17a, "Astronomical Perspectives," Gingerich expanded his class to 230 students after anticipating 150 enrollees.

In 1986-87, the only recent year for which exact figures are available, Science A-25 had 98 students. But Lewis said the course in recent years has had as few as seven or eight enrollees. Last year, fewer than 20 students took "Chemistry," she said.

In another Science A offering, Rotch Professor of Atmospheric Science MichaelMcElroy raised his class limit from 100 studentsto 160.

Neither McElroy nor Gingerich said their largeclasses necessarily stemmed from the small size ofA-25.

Lipscomb, who received a Nobel Prize in 1976,declined comment but his secretary indicated hewill continue teaching the course despite itssize.

There is no minimum enrollment for a Corecourse and the decision to continue is entirelyLipscomb's Lewis said.

Students said last week they hoped he would.Lovita T. Tandy '92 of Currier House said sheenjoyed the personal attention given by theacclaimed professor.

"I'm sorry more people didn't know about it,"she said, "because he seems very concerned aboutmaking sure that we learn in his class."

Colin V. Gallagher '91 of Mather House alsosaid he enjoyed the class, although he said itcould be intimidating.

"It's too bad there aren't more people in hiscourse," Gallagher said, "but it suits me justfine.