A decision by President Carter to promise additional deliveries of war-planes to Israel in the mid-1980s could clear the way for congressional approval of his controversial "package deal" of plane sales to Egypt, Israel and Saudi Arabia, congressional sources said last night.

Administration officials would not tell members of Congress yesterday that they were ready to make this modest compromise, but there were signs it was imminent. It could be revealed at a breakfast this morning to be attended by Secretary of State Cyrus R. Vance and Senate leaders.

White House press secretary Jody Powell yesterday left open the possibility of compromise without being specific. Informed sources said Carter had apparently not yet made the final decision on how far he could go to meet congressional concerns.

As reported last week by The Washington Post, the most likely compromise would involve a pledge by the United States to supply Israel more of the planes it has asked for after completion of the deliveries envisioned in the package deal.

This appeared yesterday to be enough to satisfy a majority of the Senate Foreign Relations Committee, which could then decide not to act on a resolution disapproving any of the plane sales. If the committee fails to act, the sales will go through.

All the avilable evidence suggested last night that Carter is on the verge of a major victory in getting the plane sales through Congress. In effect, Carter took on one of Washington's strongest political forces - the so-called pro-Israeli lobby - and he will apparently defeat it.

The best sign of Carter's prospects was the change of mood in the Foreign Relations Committee, which last week appeared inclined to vote out a resolution disapproving the sales. The prospect of defeat on the Senate floor - which Senate leaders and White House head-counters said was imminent - may have colored committee members' views.

A well-placed source on the committee said last night that "a compromise is very much on the tracks" that would make a committee vote unnecessary. That would amount to approval of the sales.

Members of the House International Relations Committee thought they might be first to hear the terms of an administration compromise at a meeting late yesterday with Warren M. Christopher, the deputy secretary of state. Christopher indicated last week he would have concrete proposals to make at yesterday's meeting, but when he arrived he had none. He spent two hours discussing all the issues with members.

The planes sale were the subject of numerous meetings and discussions on Capitol Hill yesterday, including these:

A hearing by the Foreign Relations Committee, at which former secretary of state Henry A. Kissinger endorsed the administration's plan while calling for additional planes to be sold to Israel.

Kissinger's proposals got an unexpectedly friendly hearing from the committee, the first sign yesterday that the mood in Congress had shifted perceptibly in the White House's favor. Previously, a majority of the committee seemed more concerned about the 60 F-15s Carter proposes to sell Saudi Arabia than about the quantity of Planes to be sold to Isarel.

Kissinger testified that Israel had no reason to anticipate the package deal, in which the sale of planes to it has been tied by the administration to the planes sales to Egypt and Saudi Arabia. This "is one reason I feel the Israeli part of the package should be augmented," Kissinger said.

He told the committee that the 15 F15s and 75 F16s Carter proposes to sell Israel were "at the very lowest end of the spectrum" of numbers discussed for sales to Israel in the Ford administration.

A series of consultations between Christopher and key members of Congress. Christopher was told by several, including the Senate minority leader, Howard H. Baker Jr. (R-Tenn.), that Care should raise the number of planes to be sold to Israel by 20.

Baker apparently would like to demonstrate some congressional influence on Carter's plans as the price of Republican support of the president's package deal.

Christopher's meeting with members of the House International Relations panel.

Lobbyists for the Saudi sale yesterday expressed optimism that Congress would not overturn Carter's plan. "It does look like reason will prevail," said Crawford Cook, a South Carolina public relations man hired by Saudi Arabia to promote the sale.

Cook and others who have been working in favor of the sale said yesterday the Saudis would not care if the number of planes to be sold to Israel is increased. Cook noted that the package had nothing to do with Saudi Arabia, and added that the Saudis did not expect to be able to match Israel's overall military capability.

The key to the Carter administration's strategy has been the understanding that, despite its opposition to the idea of a package deal, Israel wants its F15s and F16s, and is not prepared to sacrifice them in an effort to scuttle the package.

Last week the Israeli embassy here and key supporters of the Israeli cause tried to raise some doubt about whether this is Israel's position. One key supporter said he believed the government of Prime Minister Menechem Begin preferred no sales if the choice was all three or none.

Begin dispelled this impression Sunday in an appearance on "Meet the Press" (NBC, WRC). Asked to choose between all three Mideast countries getting planes and none of them getting planes, Begin said:

"I would prefer Israel should get them.That is my choice. I don't have any other choice."

Administration officials have acknowledged that Israel might have been able to unravel the package deal if it had withdrawn its own request for planes. The Carter administration reportedly advised the Israelis that this would not be a prudent move on their part.