Four Harvard professors will participate today in a National Day of Inquiry on Vietnam -- a giant tech-in organized by student body presidents and editors on more than 70 campuses across the country.

Speaking at Sanders Theatre will be John Kenneth Galbraith, Paul M. Warburg Professor of Economics; John K. Fairbank '29, director of the East Asian Research Center; Stanley H. Hoffman, professor of Government; and Jerome A. Cohen, professor of Law.

The Harvard participants will be linked by telephone and radio to 16 other campuses.

At a regional center in Chicago, Professor Hans J. Morgenthau of the University of Chicago and Muhammad Ali (Cassius Clay) will talk about the Vietnam war to colleges in the Midwest and West.

The National Day of Inquiry is the second step in a five-step program designed to mobilize a moderate course of opposition to the war -- completely independent of the New Left.

A petition drive and a house-to-house organization project similar to -- but unaffiliated with -- Vietnam Summer will follow the National Day of Inquiry.

Tonight's program will begin at 8:30 p.m. and be broadcast over WGBH-FM.