Pope John Paul II won a four-fifths majority of the Senate yesterday.

Eighty senators, ranging across the entire spectrum of religious and political beliefs, signed a letter to House Speaker Thomas P. (Tip) O'Neill (D-Mass.) asking him to invite the pontiff to address a joint session of Congress when he visits Washington Oct. 6 and 7.

The letter, written by Sen. John Heinz, and Episcopalian Republican from Pennsylvania, noted that Pope John Paul's stop in Washington "marks the first time in history a pope has visited this country's capital."

"As the pope is a world leader, a head of state, and has labored on the behalf of world peace and human dignity, I urge you [O'Neill] to extend to him an invitation to address a joint session of Congress," the letter said.

The Vatican is not recognized diplomatically by the United States and church officials have made it clear that the pope's visit here is a pastoral rather than a diplomatic one, though in some respects -- as in the protection he receives from the Secret Service -- he is being treated as a head of state.

Signers of yesterday's letter included Senators Edward M. Kennedy (D-Mass.) a Catholic, and Howard H. Baker (R-Tenn.), a Presbyterian; Jacob K. Javits (R-NY), a Jew, and Strom Thurmond (R-S.C.), a Baptist; Richard S. Schweiker (R-Pa.), a Central Schwenkfelder, and Samuel I. Hayakawa (R-Calif.), a Methodist.

Church officials said yesterday that it is unlikely the pope will make any major revisions in his schedule of activities here or in other cities he visits on his 7-day tour of the country.

The pontiff's itinerary in Washington includes a mass for as many as one million people on the Mall on Oct. 7, a visit to the White House and a meeting with President Carter on Oct. 6, as well as several other stops. All members of Congress are expected to be invited to the White House for the occasion.

Msgr. Raymond J. Boland, co-chairman of the papal visit committee for Washington, said yesterday, "My personal feeling is that there's not time for it [an address to Congress]. The time would have to come out of that set aside for the White House, and I can't expect that the president is going to relinquish that time to the Senate, especially when the Senators are all going down to the White House anyway."