The Reverend Billy Graham, 80 years old and suffering from Parkinson's disease, grasped the lectern before an electrified congregation in Memorial Church yesterday morning, delivering an evangelical oration tailored for the undergraduate population.

Graham, the seminal figure in American Christianity this century, was greeted by a standing room only crowd of more than 1,500--including students who had spent the night on the church's front steps to get a seat. He has visited Harvard twice before but never given a Sunday sermon here.

The celebrated preacher--who compared his visit to Harvard to that of a mule at the Kentucky Derby--spoke on "The Real Meaning of the Cross," exhorting his listeners to turn to God, confess and repent their sins and embrace the cross.

"Young people today, especially students, are searching for something they don't know what," Graham said.

Addressing the undergraduates assembled, Graham declared that even sexual intercourse is more pleasurable with "the love of Christ when you come to your marriage bed."

"You'll see a height of ecstasy," Graham said. "My wife is a believer and so am I, and we've had many such times."

Plummer Professor of Christian Morals and Minister in the Memorial Church Peter J. Gomes beamed at the enthusiasm students showed for Graham, joking that 20 years ago, the sight of undergraduates sleeping on the front steps of Memorial Church would have sent him running for cover, fearing a student protest.

"Those of you who can see and can hear, be grateful!" Gomes told the congregation.

For Graham, who was forced to cancel a visit to Harvard last spring because of illness, yesterday's trip to Harvard may be one of his last.