* Michael B. McElroy, Rotch professor of atmospheric science and chair of Harvard's earth and planetary sciences department.

* Neil L. Rudenstine, executive vice president of the Andrew W. Mellon Foundation and former provost of Princeton University.

Of the candidates remaining on the list, three are said to be the frontrunners--Feldstein, Leder and Rudenstine. The three widely differing academics, observers suggest, represent sharply contrasting visions for the future of the university.

And there have been indications in recent weeks that the committee may have reached a deadlock over the three top contenders and may be taking a closer look at some of the other scholars on the short list.

All three of the leading candidates fit a number of the criteria that the search committee described in a letter to students and alumni earlier this year--respected scholarship, administrative skill and Harvard ties. But so do most of the other candidates, and no candidate is perfect. In fact, each of the candidates currently under consideration has drawbacks.

Leader, widely rumored to be a strong contender early on in the search process, alienated some faculty members by his decision to turn down a joint appointment to the Faculty of Arts and Sciences in the early 1980s.

That fact has raised questions among some

NEIL L. RUDENSTINE

Age: 56

Occupation: Executive vice president, Andrew W. Mellon Foundation since 1987.

Education: Princeton University, B.A. 1956.

Oxford University, B.A. 1959 (Rhodes scholar).

Harvard University, M.A. 1963, Ph.D. 1964.

Academic Field: Renaissance literature

Experience: Provost, Princeton University 1977-87.