Three years ago this month, in a moment of diplomatic tension between the United States and Israel, 76 U.S. senators signed a letter to President Ford strongly backing Israel and bringing an end, for all practical purposes, to the Ford-Kissinger Middle East policy "reassessment."

In the Senate yesterday, at another crucial time for U.S. policy in the Middle East, Israel and its domestic supporters were able to muster only 44 votes to kill warplane sales to Saudi Arabia and Egypt. For the first time in many years, Israel lost a high-priority, high visibility test on the floor of Congress.

The two incidents were different in detail, but the political shift was plain to see. Last time, there was little or no countervailing argument in the Senate against a signature or a vote for Israel. This time, there is a powerful one. The word is a short one, and it was cited often yesterday: Oil.

Sen. Abraham A. Ribicoff (D-Conn.), a longtime supporter of Israel and a prominent American Jew, spoke of the changed circumstances as "these new realities." These are that Saudi Arabia has emerged as a world power with grave impact on the U.S. national interest and that Egypt, under President Anwar Sadat, has profoundly changed the Middle Eastern scene. Ribicoff argued that a strong and secure Israel is dependent on a strong United States, and "without a stable, predictable supply of oil from Saudi Arabia and the Persian Gulf, the West could face the worst depression of the industrial era."

Three years ago the United States imported 37 percent of the oil that turns its automobile and industrial engines, and 11 percent of total U.S. consumption came from Arab countries. Last year the United States imported 47 percent of its oil, according to Library of Congress data, and 20 percent of U.S. consumption came from Arab states.

Sen. John C. Stennis (D-Miss.), chairman of the Armed Services Committee, said in his speech, "It seems to me to be absolutely vital that the United States maintain its influence in an area of the world where we have become so vitally dependent for our day-to-day energy supply." Off the floor, he said simply, "The thing that makes [the vote] a must is oil."

Sen. Charles McC. Mathias Jr. (R-Md.), said "To those who ask whether oil plays a part in this decision about the plane package, I say that it does. We, ourselves, need Middle Eastern oil, but we can make do without it. Our allies cannot. Japan imports over 70 percent of its oil from the Persian Gulf area; key European countries [import] over 50 percent."

The financial importance of Saudi Arabia was also cited in debate and in the cloakrooms near the floor. According to Ribicoff, Saudi Arabia holds $20 deposits - about one-third of the vast reserves it has accumulated in recent years. Several senators spoke of the importance of the Saudi decision to insist that oil continue to be priced in dollars.

Several lawmakers in private and at least one in public expressed irritation at having been forced to choose between support for Israel and support for Saudi Arabia and Egypt. For Sen. Mike Gravel (D-Alaska), the U.S. responsibility for "world economic security" and for preventing a petroleum-led "world depression" dictated his choice for the arm sales.

In unusually explicit speech, Gravel cited the political and personal difficulties. "I, like many members of the Senate, up to now have a 100 percent voting record for Israel, and I have enjoyed the beneficence of that at the polls and in financial backing," he said, but this vote might well "kiss away" such support in the future. He said, "Some of the closest friends I have on this earth" will be lost because of his decision.

"I think this will be the watershed year of Jewish influence in this country because . . . what is happening to me, I am sure it is happening to other members of the Senate who have been loyalists to the Jewish cause in the Middle East," Gravel said.

Domestic politics, as always, had a bearing on the Senate outcome. For example, it was easier for Democrats to sign a letter for Israel in a struggle with a Republican president than to vote against a Democratic president who strongly advocated arms sales. The arms sale support of the Senate GOP leader, Howard H. Baker Jr. (Tenn.) was considered important. Sources close to Baker said he could have won major backing for his presidential hopes by opposing the sales.

While announcing their votes for the arms sales package, many senators expressed their eternal commitment to Israel and several suggested that the United States give additional arms and assurances to the Israelis as evidence that U.S. backing is strong. Support for Israel is one thing, they argued, but acting at Israel's behest to deny U.S. support to Saudi Arabia and Egypt is another.

Sen. Clifford P. Case (R-N.J.), a leader of the opposition to the arms sales, called the verbal commitment to Israel under the circumstances "a slippery word." He said there was "serious erosion" and great danger in equating U.S. ties to Israel with U.S. ties to Saudi Arabia, Egypt and the Arab world.

The Senate majority did not agree. By permitting the sale of warplanes to all three countries, the Senate put its approval on a tangible as well as symbolic form of the Middle Eastern "evenhandedness" that Israel has so long dreaded.