Carter administration intelligence analysts are increasingly concerned that Iranian military officers are positioning themselves to seize power if Prime Minister Shahpour Bakhtiar fails to form a government friendly to the military establishment, U.S. sources reported yesterday.

The private intelligence warnings reaching Washington were echoed by Bakhtiar in a newspaper interview published in Tehran yesterday.Bakhtiar told the Persian newspaper Kayhan that he was "trying my best to prevent a military coup d'etat."

Bakhtiar's failure thus far to produce a defense minister respected by the military has caused U.S. policy-makers to focus again on the Iranian army in the past two days and press for fresh reports on the prospects of a military takeover, according to U.S. officials.

In a separate move yesterday to demonstrate its concern about the impact of the continuing Iranian crisis in the Persian Gulf, the Carter administration announced that it was sending a squadron of F15 fighter bombers, the most sophisticated warplane in the Air Force's inventory, on an unusual visit to Saudi Arabia.

The visit, which State Department spokesman Hodding Carter referred to as "a highly visible fly-in," was first requested three months ago by the Saudi government, U.S. officials said, and is not directly related to the Iranian crisis.

The Saudis, initially upset by what they see as increasing Russian encroachment in the Horn of Africa and the Yemens and now deeply concerned by events in Iran, asked for the visit as a visible sign of American support for the Saudi royal family, U.S. officials said.

The visit also carries important political symbolism in Washington and is an apparent signal of the administration's resolve to go ahead with the $2.5 billion sale of 60 F15s to Saudi Arabia with deliveries to begin in 1982.

Failure of the Saudi government to support Egyptian President Anwar Sadat's efforts to sign a peace treaty with Israel has triggered suggestions on Capitol Hill that a move will be made to force reconsideration of the Senate's approval of the sale.

A training and maintenance team of up to 300 men will accompany the 12-plane squadron, which will be unarined. The squadron's flight from the United States, with refueling in Europe will take place in mid-January, U.S. officials said.

The mission appears to resemble a decision by the Kennedy administration to send a squadron of F100s to Saudi Arabia in the early phase of the Yemen civil war to send an implicit signal to foreign nations of American resolve to help protect Saudi Arabia.

Hodding Carter said the visit would be brief and "is a demonstration of the continuing close relationship between Saudi Arabia and the United States and of our interest in the security of the kingdom."

Saudi Arabia is the world's largest oil exporting country, and currently produces 10.5 million barrels a day of oil to make up for the shortfall in Iranian production. Iran was the second largest exporter until strikes shut down the oil fields last month.

In another military movement also intended in part to convey a political signal, the Pentagon disclosed Tuesday that it was temporarily increasing the number of Navy warships in the Indian Ocean and Persian Gulf areas from five to nine.

In the face of the growing threat of a military takeover that would plunge Iran into a violent eruption, U.S. officials now list maintaining some kind of governing authority in place -- with or without Shah Mohammad Reza Pahlavi -- as the primary task.

The continuing presence in Iran last night of Gen. Robert Huyser, the deputy commander of U.S. forces in Europe, was seen by some American analysts as another important sign of the administration's concern about a potential coup effort.

Huyser was dispatched by the administration to Iran last week in part to persuade Iranian generals not to oppose the Bakhtiar government, according to State Department officials.

U.S. officials disclosed yesterday that Huyser also was told to try to persuade Gen. Freydoun Jam, a respected career officer who has a reputation for being independent of the shah, to accept the defense portfolio in the government Bakhtiar presented formally to the shah on Saturday.

But Jam, reportedly convinced that the Bakhtiar government cannot survive, refused to see Huyser and left Iran for Europe over the weekend.

U.S. analysts are most disturbed by reports now reaching Washington which show a new and more intense pattern of rotation of army units around Iran. Troops with relatives and friends in one area are being deliberately reassigned to areas where they presumably know no one, according to these reports.

U.S. analysts are also disturbed that large numbers of tribesmen from Iran's remote regions, such as Baluchistan, have been moved into Tehran in recent weeks.

Positioning of units in areas where they would presumably be fighting strangers rather than friends is a classic preparatory step for the kind of armed confrontation that could take place if the army does try to seize power, according to some U.S. officials.

U.S. policymakers are reported to be pressing particularly hard for information on younger colonels and lower-ranking generals who are now known to have been urging their superiors last year for a massive and bloody response to the civilian protests against the shah.

This group, rather than the generals around the shah, may represent the greatest threat for a coup, some U.S. analysts believe.