February 21, 1984

The Internal Revenue Service is unpopular at the best of times, but lately it has sunk to some sort of new low among waiters, waitresses and managers at restaurants and bars throughout the country. The reason: a new regulation aimed at squeezing greater tax revenue out of tips. Employers are complaining about the regulation's complexity and about the costly new administrative burden they must shoulder. The employees are unhappy about a requirement that a fixed rate be used in estimating their tips, a fluctuating but critical supplement to their income. Both groups insist that an injustice is being done. ''The whole thing is really a can of worms,'' said Ronald A. Sarasin, director of government relations for the National Restaurant Association in Washington. ''And it's not fair.''

More than 2,000 Poles packed into a Roman Catholic Church in this industrial suburb of Warsaw tonight for a protest mass that represented a challenge to the authority of the Polish Primate, Jozef Cardinal Glemp. The reason for the protest was Cardinal Glemp's decision last week, under what church officials said was intense Government pressure, to transfer the Rev. Mieczyslaw Nowak, an outspoken supporter of the outlawed Solidarity trade union founded by Lech Walesa. Father Nowak was head of the St. Joseph the Worker parish in Ursus, site of a sprawling tractor factory that is one of Poland's largest industries and was once a Solidarity stronghold. A Division Within Church The protest mass, an extraordinary event in this deeply Roman Catholic nation where the authority of the hierarchy has traditionally been respected, appeared to reflect a growing division between Cardinal Glemp and many of the younger priests and laity Since the imposition of martial law in December 1981, local churches have become sanctuaries for the remaining spirit of Solidarity, reflecting what has been seen here since the end of the 18th century as the church's role as the protector of the Polish nation.

The Italian contingent of the multinational force completed its withdrawal from the Lebanese capital today. The departure of all but 100 members of the 1,385-member Italian force left about 1,300 American marines and 1,250 French soldiers protecting areas in Beirut. The remaining 100 Italians were staying behind in the port area to ''tie up loose ends,'' according to an Italian military spokesman. Marine officers said tonight that they had received orders from the Pentagon to begin loading up their combat forces. They said all the men had been told to ''get their stuff together'' and would probably begin pulling out of the bunkers Tuesday by helicopter and landing craft. They said the transfer to their ships would probably be spread over seven or eight days.

RESEARCHERS can now demonstrate that certain crucial areas of human intelligence do not decline in old age among people who are generally healthy. Moreover, although some other aspects of intelligence do dimish, the decline is relatively inconsequential and has been exaggerated in the past, the experts assert. The new research challenges beliefs long held by scientists and the public and suggests that, among people who remain physically and emotionally healthy, some of the most important forms of intellectual growth can continue well into the 80's. It also suggests that declines in intelligence can be reversed in some instances and that earlier notions about the loss of brain cells as a person ages were in error. This more optimistic view of the mental capacities of the aged emerges from a broad range of current studies, from recent literature in the field and from interviews with gerontologists, psychologists and experts in related health sciences.

''The future has been postponed, not canceled.'' - James J. Whalen, president of Ithaca College, on an unexpected surge in student applications. (C10:3.)