Ed Muskie is not a happy man. Despite the public papering-over of his differences with the Carter administration, Muskie feels he has been used and abused since he agreed to be Jimmy Carter's secretary of state.

At the same time, the professional bureaucrats at Foggy Bottom are just as unhappy with their new boss and the top aides he brought with him from the Senate.

Muskie has done some private complaining to old friends and political associates about his troubles with the Carter crowd. Here's what he has told them:

Carter is surrounded by an impenetrable coterie of Georgia cronies, and no one outside the inner circle can get through to him.

Muskie feels betrayed by Carter, who publicly promised to make him his chief foreign policy spokesman. Muskie gave up a safe Senate seat only to discover that he has been kept as far out in left field as Cyrus Vance ever was. Policy decisions were made without even consulting him.

The "third-man" speculation during the weeks before the Democratic convention made Muskie realize that he might have been the choice as an alternative to Carter or Ted Kennedy. He half suspects that Carter named him secretary of state simply to take him out of contention for the nomination.

A number of incidents contributed to Muskie's disenchantment:

In late June, on White House instructions, Muskie made a strong anti-soviet pitch to the NATO foreign ministers, who then called for "immediate, unconditional and total withdrawal" of Russian troops from Afghanistan. A month later, White House national security adviser Zbigniew Brzezinski publicly announced a more reasonable policy of containment linked with continued pursuit of detente and arms control. Muskie, although he personally agrees with a more moderate policy, was furious that Brzezinski, the Cold War hothead, was allowed to announce an apparent policy shift that undercut Muskie's earlier tough position.

Muskie was understandably upset at being frozen out of discussions that led to the change in U.S. nuclear strategy announced early this month.

Muskie feels Carter used him as a cat's paw in the decision to abstain in the United Nations from censuring Israel over the Jerusalem issue. Muskie was asked to go to the United Nations to personally withhold the vote, which brought down the wrath of the Jewish community.

Meanwhile, at Foggy Bottom, sources who are disenchanted with Muskie told my associates Joe Spear and Lucette Lagnado another side of the story.

"Since he came here, Muskie has been a part-time secretary," one top official complained. "He spends his three-day weekends in Maine and doesn't pay much attention to his work. He's a ceremonial secretary of state . . . If Carter wins the election and Muskie gets reappointed, he may get serious."

But this same source said Muskie may have blown any chance he had for reappointment by his coy refusal to reject emphatically his availability as a compromise candidate in Carter's place. Carter and the other Georgians haven't forgotten that.

Muskie's regal, free-spending senatorial habits have rankled the professionals at the State Department, who mourn for Cyrus Vance. Muskie's personal staff of five, brought over from Capitol Hill, is derided as wide-eyed rustics overwhelmed by the grandeur of their new surroundings.

Accustomed to the perks of a powerful senator, Muskie's staff has stepped on toes at Foggy Bottom by using security personnel as "go-fers," and generally not knowing "how to treat people around here." One Muskie aide appalled the bureaucrats by asking subordinates to take care of the shipment of Muskie's son's luggage to college -- a request that wouldn't have raised an eyebrow on Capitol Hill.

Muskie has also been critized for his expensive tastes in personal travel, using a small government jet to fly him to his home in Kennebunkport, Maine, for weekends. He has claimed that only half have been personal trips. For these, he is required to reimburse the government at first-class fare -- a fraction of the actual expenses of the private jet.