After a month of hesitation and reports of high-level intrigue in Tehran, Iran's new government let it be known yesterday that on Feb. 19 it will replace Ardeshir Zahedi, the shah's controversial ambassador to the United States.

The decision carries major political significance according to some analysts here. It appears to underscore the political eclipse of Shah Mohammed Reza Pahlavi and points to a changing mood in the Iranian army's leadership, which previously had insisted that Zahedi's presence in Washington was essential.

Zahedi continues to be the shah's most trusted political ally and has styled himself "the shah's ambassador" since the Iranian monarch left Iran on Jan. 16 and was replaced by the government of Prime Minister Shahpour Bakhtiar.

Since then, Zahedi has been commuting between Morocco, where the shah has settled for the time being, and various U.S. cities to look after the shah's interests and family. Opposition figures, including some diplomats from his own embassy, have accused Zahedi of trying to mount a plot to restore the shah to the throne by force.

The political turmoil in Iran has also engulfed the embassy in Washington. The majority of the embassy's estimated dozen career foreign service diplomats have walked off their jobs in a continuing series of political and professional protests or have been put on leave by Zahedi.

Divided into two groups, the dissident diplomats have appealed to the State Department and to the Foreign Ministry in Tehran to withdraw the accreditation of Zahedi and of his security chiefs, Maj. Gen. Mokhateb Rafii and Capt. Cyrus Baharmast, who took control of the embassy away from the dissidents last week in Zahedi's absence.

Reports of the embassy takeover touched off demonstrations against Zahedi in the Foreign Ministry in Tehran, according to Iranian sources. The reports may have led to a statement by Bakhtiar's foreign minister, Ahmed Mir-Fendereskei, that Zahedi's tenure in Washington is being "terminated."

The embassy's press counselor, Ali Akbar Tabatabai, said that the embassy had been informed that Zahedi's resignation has been accepted by the Foreign Ministry and that his last day as ambassador would be Feb. 19. Zahedi reportedly was in California yesterday.

The Foreign Ministry advised the embassy two weeks ago that Zahedi's resignation had been accepted, but withdrew the announcement of it after military leaders intervened with Bakhtiar's government and asked that Zahedi be kept on for the time being, according to diplomatic sources.

State Department spokeswoman Jill Schuker said the administration had no reason to doubt press accounts of the foreign minister's statements, but could give no date for the resignation.