For a good many centuries people have flocked to the cathedral at Canterbury - at first, because they were sick and thought a pilgrimage would help them, and in more recent years because they were well, and had a lively sense of awe for the beauty and history of the most famous church in England.

Unfortunately, time has weathered away too much of the old Caen stone and the acids of modernity (as Walter Lippmann used to say of the modern world in general) have severely damaged the stained glass. (The glass is the most notable in England, much of it from the 12th century, the finest period for glass.)

A Washington benefit tonight will help along an appeal that was launched in 1973 to raise $6 million worldwide for a long-range preservation and repair project.

The Prince of Wales took on the job of president of the trustees for the appeal and narrated a color film (shown recently at the Folger Shakespeare Library) showing the need for repairs, and conveying a sense that the great building is a legacy to the world, not just to Anglicans.

Committees sprang up to help raise money. And the performance of the Boston Symphony tonight at the Kennedy Center will benefit Canterbury - it is expected that about $25,000 will be realized by this plus many small gifts from people who simply heard the church was in poor repair and needed money and just sent in a couple of dollars.

Leaders in the Washington fund-raising are Lady Margretta Jamieson, chairman; Mrs. Robert Low Bacon, Fraser Barron, Lucius D. Battle, Samuel E. Belt 3d, Col. Robert F. Evans, J. William Fulbright, Constance Mellon, John M. Patterson and Mrs. John A. Pope.

Before the concert, dinners for ticket holders will be given by various members of that committee, and by Mrs. Forbes Hall, the J. Burke Wilkinsons and the Hugh Newell Jacobsens.

The evening's soloist, Peter Serkin, will be guest of honor at a reception after the concert given by the Huntington Blocks, and the conductor, Seiji Ozawa, at a party given by Mrs. Bacon.