Sen. Frank Church (D-Idaho) and other members of the Senate Foreign Relations Committee are trying to persuade the Carter administration to again postpone the sale of 60 F-15 fighter-bombers to Saudi Arabia.

The Saudis are eager to purchase the F-15, one of the best and most sophisticated fighter aircraft in the world, and the administration has decided it must sell them the plane as a demonstration of U.S. concern for Saudi Arabia, a crucial U.S. ally.

But members of the so-called "Israeli lobby" in Washington and many senators have expressed opposition to the sale. In a draft letter that Church has circulated among colleagues, he calls the proposed sale "unwise" because it would give the Saudis a weapon with which they could attack Israel, and because a sale at this time might jeopardize the delicate, now-suspended Mideast peace talks.

A senior administration official said yesterday that the administration hopes to carry out the sale in conjunction with sales to Israel and Egypt. A "package deal" of this kind would be a response to the charge that a sale of F-15s to Saudi Arabia would disrupt the military balance in the Middle East, the official said.

Israel has also asked to buy F-15s - at least 20 of them. Ezer Weizman, Israel's defense minister, is due to visit Washington Thursday to renew Israeli pressure for more U.S. arms.

An aide to Church said last night that the idea of a "package deal" had not been spelled out to the senator by the administration.

Church strongly believes, the aide said, that this is a most inappropriate time to discuss such a big arms sale to the Saudis, given the touchy peace negotiations between Israel and Egypt.

The letter Church circulated included no friendly reference to the Saudis. When the State Department learned this yesterday, it urged that the letter be amended so as not to offend Saudi sensibilities, even if it continues to call for no sale of F-15s.

"It would be most unfortunate for the Foreign Relations Committee to go on record with a letter that the Saudis would regard as hostile to them," a department official said.

Church apparently is willing to modify the letter to take Saudi feelings into account.

Half a dozen senators had agreed to sign the letter by last night, and Church's staff expressed hope that a majority of the committee would sign a revised version.

The purpose of the letter is to persuade the administration not to submit formal notification of the proposed sale to Congress. This notification is the first formal step toward an arms sale under a new law that gives Congress the right to veto a proposed arms sale.

Church apparently hopes to demonstrate that enough senators oppose the F-15 sale to raise the danger of a veto of the deal.

Last summer, the threat of opposition in the Senate convinced the administration to hold off on formal notification of its intention to sell the F-15s.

The Ford administration originally decided that this sale was in the American interest, and the Carter administration renewed this decision. Saudi Arabia was one of President Carter's stops on his world tour, and Saudi-American relations are extremely close at the present time.

But friends of Israel on Capitol Hill and elsewhere have persistently opposed any arms sales to the Saudis that they thought might alter the Mid-east military situation.

Transferring F-15s to the Saudi air force "would seriously enlarge the threat of an aerial strike against Israeli military and civilian targets," Church wrote in the draft letter he circulated yesterday. He also mentioned the possibility that Saudi Arabia might give the planes to another Arab country during an emergency.