Despite two months of American protests, West Germany has accepted as its new Iranian ambassador in Bonn a man the United States claims was involved in the 1979 seizure of the U.S. Embassy in Tehran and the subsequent 444-day captivity of American diplomats.

State Department spokesman Charles E. Redman said yesterday the United States has "persuasive information" that Mehdi Ahari Mostafavi "was associated with the taking of American hostages at the U.S. Embassy in Tehran."

For this reason, Redman added, the United States has complained to Bonn several times since August when it learned that Mostafavi, who had been Iranian ambassador to Austria, was being transferred to West Germany.

Redman said Bonn already had agreed to accept Mostafavi when Washington first protested the appointment. The spokesman added: "We believe that this whole incident points up the need for better and earlier and more timely coordination and cooperation among countries of the world when we are dealing with other nations known to be involved in sponsoring terrorism."

West German diplomatic sources, who asked not to be identified, confirmed that their government had accepted Mostafavi before the U.S. protests. They added that, in Bonn's view, the evidence presented by Washington about his alleged terrorist connections was not sufficiently persuasive.

The incident was the second time this year when Bonn and Washington, normally close allies, have differed over the handling of people allegedly involved in terrorism.

In January, the Germans arrested Mohammed Ali Hamadei, a Lebanese wanted by the United States for the murder of a U.S. Navy diver, Robert Stethem, during the 1985 hijacking of a Trans World Airlines jet in Beirut. After months of negotiation, Bonn rejected a U.S. request for Hamadei's extradition and said he would be tried in West Germany. The decision caused widespread speculation that Bonn was fearful of terrorist retaliation against its citizens, including two West Germans who were being held hostage in Lebanon.

U.S. officials, speaking privately about the latest incident, disputed the West German contention that reversing the decision to accept Mostafavi would have caused an unjustifiably awkward diplomatic incident. These officials said that because he has not yet presented his credentials to West German President Richard von Weizsaecker, it would have been a simple matter for Bonn to tell Tehran it had changed its mind.