After explaining to Zbigniew Brzezinski that he wanted to lunch alone with Henry Kissinger last week, President Carter suddenly changed his mind and invited not Brzenzinski but the top White House aide, Hamilton Jordan, to join him.

In an earlier day, such treatment of the President's National Security Adviser would have been deemed cavalier. It is unthinkable that predecessors of Brzezinski such as Mc George Bundy, Walt W. ROstow or the fabled Kissinger would have accepted it.

In the Carter White House, however, Brzezinski not only blithely allowed himself to be odd man out but seemed unperturbed. "Remember," one White, House aide told us in trying to establish a rationale for Brzezinski's exclusion, "there's a new attitude in the Carter White House - an attitude of mutual trust."

Perhaps. But the exclusion of Brzezinski was a symbolic act that points up this danger: lack of overall foreign policy coordination tha has led to flatly contradictory positions by burequcratic interest competing for Carter's favor, the result is bewilderment in foreign embassies and among the bureaucrats themselves.

It would be grossly unfair to blame this on Brzezinski. It is the President who sets the style and dictates the way he wants things done. The handling of the Carter-Kissinger luncheon is a case in point.

Brzezinski's exclusion cannot be explained, as some White House aides are saying, by the "limited" subject matter: the President's wooing of Kissinger to support the Panama Canal Treaty. In fact, the two men ranged over many issues foar removed from Panama. Jordan, in charge of rounding up enought senators for retification, took an active role in the conversation.

Brzezinski should by right have been there both to protect the President from possible end runs by the formidable Kissinger and to soak up a little of Kissinger's foreign-policy lore. Most important, word of his absence immediately fed the capital's romor mills, already choked with tales of Brzezinski's limited authority over the bureaucracy. Herewith a sampler.

Item: Central Intelligence Director Stansfield Turner failed to coordinate with Brezezinski the CIA's strong opposition to the proposed U.S. sale to Iran of AWACS (early-warning aircraft). A letter from Turner to Congress that warned against the sale for security reasons damaged the administration's real position: strong support of the sale.

Item: One of Turner's national intellingence officers told the Senate Foreign Relations Committee behind closed doors in June that withdrawing American troops from South Korea would incur "unacceptable risks" to the United States. A few hours later, Gen. George Brown, chairman of the Joint Chiefs of Staff, and Philip Habib, Undersecretary of State, baffled the same committee by saying the administration favors the troop pullout.

Item: By agreement with presidential press secretary Jody Powell, Assitant Secretary of State Richard Holbrooke on Aug. 18 formally briefed the press on Secretary of State Cyrus Vance's China trip. The next day, Brzezinski summoned a dozen reporters for a "worldwide" briefing - which turned into a second Vance-to-China analysis. There was no coordination with the State Department, of both the President and Brzezinski for maladroit planning.

A classic case: the deliberately hostile reception here for then-Prime Minister Yitzhak Rabin shortly before the Israeli election last spring, followed by an open-arms reception for his successor, Menachem Begin. This seeming preference for Begin, who is infinitely more menacing to U.S. interests in the Mideast than Rabin, was more a result of thoughtlessness than intention.

"We get a hip-shot from Zbig saying "this is what the President wants,' but it's not thought through at all," one middle-level State Department official told us. These hip-shots are undoubtedly fired by the President himself, but they are ricocheting on his adviser for national security.