The United States is taking steps to shore up the new civilian government of Prime Minister Shahpour Bakhtiar and eliminate the threat of a military coup, informed sources said today.

American officials here recognize the fragility of the Bakhtiar government, the diplomatic sources said, but the fragility of the Bakhtiar government, the diplomatic source said, but are trying to support it by countering the threat of a rear-guard action by hard-line pro-shah Iranians following the monarch's departure, which is expected in a matter of days.

The Bakhtiar Cabinet, presented to Shah Mohammed Reza Pahlavi on Saturday, also faces the same problems of street demonstrations and widespread strikes that plagued the previous military and civilian administrations. But in an apparent attempt to create solidarity between in and the demonstrators, the new government threw in its lot with an opposition call for another national day of mourning Monday.

In the troubled oil fields of southwastern Iran, production continued to hover around 250,000 barrels a day, despite a reported agreement between striking oil workers and an opposition delegation to produce and refine enough crude to meet domestic needs. Current output is about 4 percent of capacity and far below the approximately 600,000 barrels needed for home consumption.

Against this backdrop, one purpose of the visit here by the deputy commander of U.S. forces in Europe, Gen. Robert Huyser, is to prompt senior Iranian officers to support the Bakhtiar government despite their distaste for its self-described liberal and social democratic tendencies, the sources said.

They also said Ardeshir Zahedi, the Iranian ambassador to Washington, is being discouraged from trying to rally the hard-liners or impede the shah's plan to leave the country for an openended vacation -- a move regarded as vital to the Bakhtiar government's slim chances of survival.

Zahedi, one of the shah's staunchest supporters, is to leave Iran by the end of the week, although his future as ambassador to Washington under the Bakhtiar administration is in doubt. In the past, ambassadors have normally been appointed by the shah himself. Thus, the case of Zahedi is likely to become an important test of Bakhtiar's promise that the new goverment will exercise full powers and relegate the monarychy to figurehead status, deplomatic sources said.

Zahedi also is seen as a key figure in a hard-line pro-shah group including several top generals that has been resisting the Bakhtiar solution. His absence would reduce the threat to the new government, the sources said.

Huyser has been conferring with senior Iranian officers, among them the new chief of staff. His mission has not been officially specified, but informed sources indicated that part of it is to encourage the generals to go along with the Bakhtiar government, which Washington has expressed readiness to back.

Huyser, who arrived late Friday, is known to have good relations with a number of Iranian generals. He has visited Iran regularly in recent years.

Another aim of his visit is to resolve financing snage that have developed inrecent months involving sales of military equipment to Iran and other U.S. contracts with the Iranian War Ministry, sources said. Because of paralysis in the local backing system, strikes and overriding political problems, the government has defaulted on contract payments for several projects, including a now-defunct helicopter coproduction scheme.

Huyser has been successful in getting some new funds moved into other wants to buy, the sources said. There was no confirmation of reports that his visit also is connected with American efforts to sharply pare down the U.S. military advisory mission here or tighten security for advanced U.S. equipment already delivered to Iran.

Despite the U.S. concerns, the most immediate threat to the Bakhtiar government appears to come from circumstances which the United States is in no position to control.

Small mobs of anti-shah demonstrators burned debris and set up barricades in a number of streets in downtown Tehran today after a lull of several days, showing that their attitude toward the authorities remains unchanged.

Contingents of army and air force troops fired tear gas and rifle shots to disperse mobs in several parts of the city. Opposition sources reported at least three demonstrators were wounded, although most of the shooting seemed to be into the air.

Troops dispersed a crowd of several thousand people at a Tehran hospital where the opposition National Front had scheduled a rally. Demonstrations also were reported in several provincial towns.

Slogans against the shah and Bakhtiar were written on walls and shouted by the street protesters in Tehran. "We keep saying that we dof't want the donkey, but all they do it just keep changing its saddle," one demonstrator said.

Shops, offices and banks were largely shut in observance of a strike called by the National Front and, in a new twist, supported by the government. The Bakhtiar administration also backed another strike and the "naktional day of mourning" called for Monday by exiled religious opposition leader, Ayatollah Ruhollah Khomeini. The official Iran Radio said music porgrams would be suspended for the second straight day to commemorate victims of army shootings in recent months.

Iranian newspapers, reappearing for the second day after a two-month strike, reported that former government officials and wealthy businessmen recently arrested on corruption and malfeasance charges will soon be tried, and that as many as 15 face execution.

One newspaper printed front-page photographs of five prisoners in their jail cells, including former prime minister Amir Abbas Hoveyda and former information minister Dariush Homayoun.