It may take a while to figure out whether the vote against the sale of AWACS to Saudi Arabia was a vote against Ronald Reagan or against Jimmy Carter.

The former president announced his advocacy of the sale on the eve of the massive rejection in the House. It was like old times. He muddied the waters and set the teeth of his fellow Democrats on edge.

After the 3-to-1 victory for AWACS foes, an exulting Rep. Benjamin S. Rosenthal (D-N.Y.) said of Carter, "He helped."

Democrats were annoyed that Carter had taken the "support-your-president" line from the Vietnam years in saying, characteristically, that while he did not think it "wise" to sell the aircraft to the Saudis, he was for it, because once the president has made a commitment it is the duty of Congress to back him up.

"Yes," snorted House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), who was predicting a Reagan rout on the matter. "Carter said if the president goes out on a limb, we're supposed to follow him."

Democratic National Committee Chairman Charles T. Manatt, who has raised a fortune on opposition to the AWACS sale, announced that Carter, the titular leader of the Democratic Party, was speaking for himself.

At his morning briefing, O'Neill rather pointedly referred to himself as "the leader of my party," just in case anyone thought Carter was a spokesman on the one question that has unified the Democrats.

On Capitol Hill, the memory of western Democratic seats narrowly lost because of Carter's premature concession to Ronald Reagan still burn. He left no constituency behind, because his presidency, like his visit, never quite came into focus.

He announced at his news conference that he had not come to criticize the president, and then he did on the domestic side. He called Reagan's presidency "an aberration on the political scene," which is, of course, precisely how many Democrats regard the Carter years.

Having said that, he proceeded to the White House, blew kisses upon alighting at the portico, and sat down to discuss the weather, within earshot of the press, with Ronald Reagan in the Oval Office.

When he came out, he declined to say what he and Reagan had talked about when they were alone. In answer to a question, about the man he once said would divide the country, "We have always gotten along very well."

Carter arrived just as Sen. Larry Pressler (R-S.D.), a freshman, was leaving after a seance on AWACS. Pressler, a signer of a protest letter, couldn't get his White House calls returned during August, when he wanted to negotiate. But since the death of Sadat, whose coffin the Republicans have used as a soapbox for the sale, and since Pressler made a suggestion that we provide Israel with offsetting radar and jamming equipment, he has been immersed in attention.

Pressler was of far more consequence to Reagan than was Carter. The president conceded the House to the enemy and sent no lobbyists. He expects to recoup in the Senate, and Pressler is a key figure.

Carter was hardly mentioned in the debate. A fellow southerner, Rep. Buddy Roemer (D-La.), who votes with the Boll Weevils for Reagan's domestic programs, was one of the few who bothered to speak of the array of ex-officeholders, and architects of previous foreign-policy disasters, who have been called forth to persuade Congress to vote against powerful Jewish constituencies in the interests of making Reagan look good.

"No matter what Jimmy Carter or Henry Kissinger say," Roemer raged, "Our national interest is to vote against this sale."

Republican members who are said to harbor higher ambitions took the same note. Clarence J. Brown of Ohio, Jack Kemp of New York and John H. Rousselot of California all deserted the leader of their party.

Said Kemp, usually a slavish follower, "I find it incomprehensible that the U.S. would sell arms to the No. 1 enemy of Camp David."

One hundred seven Republicans joined him, making the rejection bipartisan.

Some Democrats are overreacting to the Carter trip. The stay at Government House on Lafayette Square, the visit to the National Committee, the lunch on Capitol Hill have led to morbid suspicions that the man from Plains is planning a comeback. Resurrection is in the air. Richard M. Nixon, who quit office one step ahead of the sheriff, is careening around the Middle East, talking to potentates and preparing to report to the White House.

Jimmy Carter, who suffered a staggering defeat in November's election, may feel that his attendance at Sadat's funeral has transformed him in popular regard. But the Democrats are another story. Their fling with an "outsider" ended in what Rosenthal calls "an American disaster." The maddening intervention on AWACS is just another illustration that he was never one of them.

Ronald Reagan is doubtless glad that Carter came. At least he can share the blame for his first crushing foreign-policy defeat in the House with a predecessor who taught him everything he knows about how not to deal with Congress.