In Washington's real-life political theater, Sen. Frank Church (D-Idaho) has suddenly been recast as a leading hard-liner, an abrupt reversal that has surprised his colleagues and evidently discomforted the senator himself.

Church's new role has come in the Senate debate, which he initiated 12 days ago, over Soviet troops in Cuba.

Yesterday, a colleague who has stood with Church in countries previous dramas made a point of diassociation. George McGovern (D-S.D.), a fellow western liberal in the past sharply criticized "those who are issuing ultimatiums to the Soviets to bring their troops home."

This group was also criticized by Sen. Joseph R. Biden Jr. (D-Del.), another liberal on the Foreign Relations Committee, and over the weekend by Sen. Robert C. Byrd (D-W.Va.), the majority leader.

Many of Church's colleagues attribute his new position to politics. A liberal Democratic senator said, "I think it's called survival as he perceives it. I think he's making a mistake."

Church rejects any suggestion of politics, asserting that he has consistently opposed Soviet use of Cuba for potentially dangerous military purposes, and that he would have taken the same position if he weren't a candidate for reelection next year and already the target of sharp attacks from the political right wing in Idaho.

Others in the Senate note that Church chose to make the first official announcement of the presence of a Soviet combat "brigade" in Cuba while on a trip to Idaho, and that Church has appeared nervous all year about reelection.

One points seems undisputable: given his liberal credentials and firm support for the pending SALT II, Church's prediction that the arms treaty won't pass the Senate unless the Soviets withdraw this "brigade" from Cuba provided many moderate and conservative senators a starting point for their own rhetoric on the issue. "Church set the standard," as an administration official put it.

Church insists that the prediction was only his reading of the mood in the Senate. He has also said that he personally thinks the troops should be withdrawn from Cuba before the Senate votes on SALT II.

"The Soviets have insinuated a combat brigade into Cuba and sought to conceal it from the United States for a period of years," Church said in an interview yesterday. "The Russians must have know from the beginning that the existence of the brigade would be discovered and that when that time came there would be another testing of American will and resolve."

Church says the United States should now meet this test squarely by forcing the troops out of Cuba through negotiations.

Church and sources close to him suggest that when Undersecretary of State David Newsom phoned Church in Idaho on Aug. 30, he left him the impression that the Carter administration planned to let news of the Soviet brigade in Cuba leak to the press, without a government announcement. Church says he felt this was an inappropriate way for such an important development to become public knowledge, and decided to make the announcement himself, after informing Secretary of State Cyrus R. Vance of his plans.

In fact the administration had already decided to make an announcement from the State Department the very next day, according to government sources, but apparently neither Newsom or Vance told this to Church.

The administration and fellow liberals in the Senate have faulted Church not for making the announcement, but for predicting that the Soviets would have to withdraw the troops entirely before SALT II could be passed. Church says this was his sense of the politics involved.

Though numerous conservatives and Republicans have endorsed or repeated Church's prediction, fellow liberals have not.

Jacob Javits (N.Y.), ranking Republican on the Foreign Relations Committee that Church chairs, has pointedly distinguished his position from Church's in public and private. Javits has said that he would require a satisfactory resolution of the Soviets-in-Cuba issue before voting on SALT II but has not specifically demanded a Soviet withdrawal.

McGovern's statement yesterday said, "how can we seriously argue that we have the right to deploy 500,000 American troops around the world but that the Soviets have not right to station troops in Cuba?" And, McGovern asked, what if the Soviets responded to demands for their withdrawal from Cuba with demands for American withdrawals from other countries? McGovern praised President Carter for "keeping cool over the Soviet troop deployment in Cuba."

Church said yesterday he still had not decided whether the Foreign Relations Committee should delay its markup of SALT because of the troops issue.