An American hostage in Tehran, expressing the frustrations and pressures of more than three months of confinement, has pleaded for U.S. government action, saying he fears that he and his fellow hostages may be considered "expendable."

"Our future is very uncertain, and I am not overdramatizing when I say our very lives hang in the balance," State Department budget officer Bruce W. German, of Kensington, Md., said in a letter received yesterday by The Washington Post.

"Needless to say, we have become rather bitter, disillusioned and frustrated, because we believe that we are victims of poor judgment and lack of foresight," on the part of the U.S. added German, 43.

His letter, dated Feb. 7, indicated that the hostages remain cut off from news. He said "the shah is still in the U.S," and described the deposed monarch's alleged presence in this country as "something which totally defies logic."

Former shah Mohammad Reza Pahlavi left the United States for the Panamanian island of Contadora Dec. 15 -- nearly two months before German wrote. Yesterday a State Department official called it "criminal" that the Iranian militants have not informed their American captives that the deposed shah is no longer in the United States.

German's hand-printed two-page letter to The Post was among 136 letters from the hostages that were brought back to the United States by American Indian activist John Thomas. Thomas, who arrived in New York Monday, recently started an informal "hostage mail exchange service" for the captives and their families.

German's wife and the State Department official said yesterday that they had no reason to doubt the authenticity of the letter received by The Post. Marge German said she had been told by her husband in a letter that he also "was writing . . . to The Post."

In his Feb. 7 letter, German expressed sympathy for the militants' views and skepticism about U.S. government situation. In this respect, his comments resembled those of other hostages in letters and broadcast statements. c

The State Department official said the political views expressed by German indicated that he apparently had been influenced by his captors. But the official added that it is unclear whether German wrote the letter under explicit direction or whether he now accepts some of the militants' views.

"We certainly do no agree with the methods used, such as disregarding diplomatic immunity, but we do sympathize and understand the motives of the Moslem students," German wrote. "They firmly believe the shah was a tyrant and guilty of despicable crimes against the human rights of his former subjects; and some of us have seen overwhelming evidence to support these charges."

German also wrote: "The majority of the hostages know that the shah should never have been allowed to enter the United States, regardless of the reasons given. Certain people, political-interest groups and lobbyists, would have people believe that the U.S. owed the shah the right to American medical care.

"Unfortunately, months prior to our capture, it was speculated in Washington that if the shah entered the U.S. for any purpose, this embassy might have serious difficulties, and possibly even be overrun. We wonder, therefore, why we were not forewarened, and later, adequately protected, once the decision was made to give the shah entry into the U.S.? Moreover, who made the decision? Kissinger, Rockefeller?"

German said the Carter administration "is reluctant to consider returning the shah [to Iran] because of certain things he might reveal; things which could prove to be very embarrassing, to say the least."

The State Department official, while citing the militants' apparent influence on German, stressed that German stopped short of voicing many of the militants' contentions.His letter, the official noted, contained no reference to alleged U.S. spying in Iran.

German, whose family has lived in Montgomery County for 19 years, arrived in Tehran five weeks before the Nov. 4 takeover of the U.S. Embassy, to begin an 18-month State Department assignment, according to his wife.

She received several letters from her husband yesterday. In these, she said, he asked about their three children and seemed "hopeful."

His letter to The Post, however, indicated a mood of isolation and some dispair.

"We have no idea what, if anything, is being done on our behalf," he wrote. Then he proposed several ideas, including the former shah's extradition to Iran for trial or a review of charges against the deposed shah by the International Court of Justice or a U.N. agency.