The growing impression that the United States would use military force to protect Saudi Arabia's oil fields against outside threats was given fresh support yesterday by two of the leading figures in U.S. foreign policy circles.

That message was underscored by Secretary of State Cyrus R. Vance and Sen. Frank Church (D-Idaho), chairman of the Senate Foreign Relations Committee, in separate television interviews.

Although both qualified their statements very carefully, they also made unmistakably clear that the U.S. stake in Saudi Arabian oil supplies is so important it could justify a reversal of America's post-Vietnam reluctance to become involved in foreign military adventures.

During recent weeks, the tumultuous rush of events in the Middle East -- the internal upheaval in Iran, the Arab-world hostility toward the Egyptian-Israeli peace accord, the fighting between South and North Yemen -- has caused such Carter administration leaders as Defense Secretary Harold Brown and Energy Secretary James R. Schlesinger to cite the need for protecting the flow of oil from that region to the West.

Last week, a middle-level State Department official, Deputy Assistant Secretary William R. Crawford, caused a sensation before a House subcommittee when he gave testimony implying that the administration would intervene militarily against a threat to Saudi Arabia, America's largest oil supplier.

Yesterday, Vance was asked about these statements during his appearance on "Face the Nation" (CBS, WDVM). He replied that it was "premature to speculate about hypothetical situations" and said that, if a situation jeopardizing Saudi Arabia arose, President Carter would deal with it in strict accordance with constitutional processes.

But Vance added pointedly: "There is no question that we have vital interests in the area. We consider the territorial integrity and security of Saudi Arabia a matter of fundamental interest to the United States. We're talking about the stability of the region, which is important not just to the United States but to the world."

Church was even more direct in an interview on "Issues and Answers" (ABC, WJLA). He said he believed the United States would be willing "to commit American forces" to counter aggression that might be launched against Saudi Arabia by an outside power like the Soviet Union.

However, Church drew a distinction between what he called "external and internal threats." He noted that an army of 700,000 couldn't save the shah of Iran's government when that country was seized by internal anarchy, and said: "I would oppose the commitment of American troops in cases where they could be of no use."

On another matter involving Saudi Arabia -- whether it can be induced to support the Egyptian-Israeli peace agreement -- Vance and Church took somewhat different tacks.

A top-level administration team including Carter's national security affairs adviser, Zbigniew Brzezinski, yesterday completed visits to Saudi Arabia and Jordan in an effort to gain at least the tacit support of these two countries for the peace treaty. The administration is particularly concerned that Saudi Arabia not cut the $2 billion it contributes annually to the financially hard-pressed Egyptian government.

In discussing the still unclear Saudi reaction to the peace agreement, Vance cautioned patience. He said, "We have made clear to the Saudis that we consider the treaty the cornerstone of a Middle East peace," but added that it is "too early to tell" how the agreement will affect Saudi-Egyptian relations.

Church, who previously has said that Saudi coolness toward the Middle East peace drive could cause the United States to reconsider the sale of F15 jets to Saudi Arabia, said, "I think we should make it plain to them that this special relationship is a two-way street."

"What I have called for," he added, "is not for the Saudis to come front and center, not for them to endorse our peace initiative or embrace the Camp David accords, but at least in a discreet way not to undertake to sabotage our peace effort."

Church was similarly blunt in discussing Jordan's King Hussein, saying: "I don't think King Hussein should expect our continuing largess as a matter of course, regardless of the attitude he takes... or if he decides to do everything he can to sabotage peace in the Middle East.

"I don't think it advances our interests to leave that impression with King Hussein," Church continued and, in a reference to Brzezinski's mission, he added: "Indeed, I do not think the president intends to. I believe this mission is going to be the most plain-spoken mission we have sent to these two countries, and I think it is high time."

Church, whose committee must pass on foreign military assistance requests, also tossed a warning flag in the path of suggestions that the United States might now start giving massive arms aid to Egypt to turn it into a replacement for Iran as a western-oriented military bulwark in the Middle East.

While conceding that Egypt does require some limited U.S. military aid, he said: "But I would be very much opposed to this 'pie in the sky' talk, this grandiose talk of making Egypt another Iran -- a policeman of the Middle East. We should have learned from the Iranian experience what a futile objective that is and not repeat the experience with Egypt."

On another front yesterday, Israeli and Egyptian officials met here to start completing final details of Israel's withdrawal from the Sinai Peninsula as part of their impending peace agreement.

Israeli Defense Minister Ezer Weizman, appearing on "Meet the Press" (NBC, WRC), said that, as a good-faith gesture, Israel might speed its withdrawal from El Arish, the major populated area of the Sinai. Under terms of the peace agreement, Israel has nine months to withdraw beyond El Arish.

Weizman also conceded that there are continuing disagreements between Washington and his government about how much the United States will pay to defray the costs of Israel's Sinai withdrawal. The Israelis estimate these costs at between $3.5 billion and $4 billion, but the administration wants to keep a cap of $2.5 billion on the U.S. contribution.

Nevertheless, Weizman said, the disagreement will not cause any delays in the expected signing of the peace treaty here next week. In fact, Weizman added, he expects to reach agreement with Defense Secretary Brown on the size of the U.S. contribution before Weizman leaves for Israel today, and he said: "If I come out of here a little less happy than I think I should, this will not affect the signature next week."