The State Department has taken over the vacant embassies of Iran, Cambodia and Vietnam, and after making extensive renovations will rent out the three diplomatic properties, officials said yesterday.

State also has requested permission from the Treasury Department to pay for the repairs out of impounded funds of the three governments. Treasury sources said that permission has been granted to use Vietnamese funds, but that the two other requests are still under review.

The three embassy buildings, formerly occupied by countries that no longer have diplomatic relations with the United States, have fallen into disrepair and need to be refurbished "before they disintegrate before our eyes," said Harvey Buffalo, deputy director of the State Department's office of foreign missions.

The State Department is acting under authority given it in legislation passed last year setting up the office of foreign missions, which oversees diplomatic property in Washington.

The secretary of state was given the responsibility to protect and preserve the property of foreign missions here and, if desired, sell the property one year after diplomatic relations ended.

Instead of selling these three embassies, State has decided to hold them "until such time as relations are reestablished and then they would be reverted back," Buffalo said. "Obviously there will be some linkage with our properties" in the affected countries.

The former Iranian Embassy on Massachusetts Avenue NW, once the site of splendid parties given by the shah's emissaries, was closed down when the Carter administration broke diplomatic relations with the Islamic government of the Ayatollah Khomeini in April 1980.

A diplomatic note was sent to the Iranian Interests Section at the Algerian Embassy here early this year informing officials of the decision to restore the embassy and six other properties the Iranian government owns and then to rent them out, a State Department official said.

The Iranians made no reply, and an official at the interests section said yesterday that "we are not authorized to make any comment, no matter how much I would like to."

Farzadi Darui, a member of the anti-Khomeini Iran Freedom Foundation, which keeps unofficial tabs on local developments affecting Iran, said the move was "a surprise to us."

Although the United States has no relations with Iran, it recognizes that its government still is the legal owner of the embassy and the six residences it is taking over, Buffalo said.

A moving van was parked in front of the embassy on Wednesday. Buffalo said furniture that is "not of historic nature or antique" will be auctioned off and the proceeds will help pay for the repairs.

The U.S. Embassy in Tehran, which was the site of the year-long hostage crisis, is still under the control of Iranian revolutionary guards, officials said. A recent advertisement in a Tehran newspaper solicited students for a new school operated by revolutionary guards. Its location was given as "the former den of spies"--a description applied to the embassy by militant Iranians during the hostage crisis.

The Vietnamese Embassy is in the worst condition, Buffalo said. He estimated it will cost about $500,000 to repair the building.

As was the case with Iranian officials, the Vietnamese were notified of State's plans for their embassy on R Street NW, which has been empty since Saigon was overrun by communist forces in April 1975. The Vietnamese did not reply, a State Department official said.

No attempt was made to inform Cambodian government officials about the rental plans for their former embassy on 16th Street NW, which has not been occupied since communist forces took over there in April 1975, the official said.

The former residence of the Cambodian ambassador, which had been vandalized, also will be rented. Preparatory cleaning and clearing began on that building a couple of weeks ago, Buffalo said.

The State Department is soliciting bids for the renovation work on the buildings and was unable to give an estimate of the total cost for repairing the properties. "But the damage is so great, we are going to need a lot of money," Buffalo said, adding that leaky roofs were a problem in some cases.

"It's good for the building and for the neighbors who complained a lot," said another State Department official. "It's hard to maintain an empty building. I think it's good for everybody."

So far, all prospective tenants are welcome. "At this point in time we haven't ruled anyone out," Buffalo said.