Since that night in August, when he called the press into his Boise living room, Sen. Frank Church's act has been the gleeful talk of the political circus that is Washington.

Church (D-Idaho) that night made the starting disclosure of a Soviet combat brigade in Cuba, and demanded its quick withdrawal. The full ramifications have yet to unfold, but one thing is clear:

Around the Senate, in the political salons, in the press, in reaction from Carter administration officials and back in idaho, Church is being perceived as an apostate who clumsily abandoned principles of moderation to save himself from election disaster next year.

Not only is there the perception. There is a sense in some of these quarters, particularly around the Senate, of pleasure in seeing Frank Church squirm.

Because of his quick linkage of the troop issue to the strategic arms treaty debate, Church is being viewed as the worst kind of brigand -- the opportunist who puts his electoral fortune ahead of all else, rushing to make constituents believe he is something other than his real self. A hardliner who is not.

Church, predictably, does not see it that way, although he concedes, with alacrity, that he "lives on a political stage, as everyone else."

Public interpretations of Church's actions are abetted by the election-year undulations in Church's voting record over his long Senate career -- more conservative at election time, more liberal in the off years, if the rating sheets from the American Conservative Union and Americans for Democratic Action have meaning.

This year he voted against Senate confirmation of federal appeals court nominees Patricia Wald and Abner Mikva, liberal types whose scalps were avidly sought by the anti-abortion and handgun lobbies. Gun control and abortion are burning issues in Idaho.

What Frank Church did in Boise on Aug. 30 was this:

He hurriedly called a news conference to announce to the world that U.S. intelligence had confirmed the presence in cuba of a soviet combat brigade. President Carter should call for its removal, he said.

Aside from the fact that Church is ivolved in a savagely bitter reelection campaign, aside from the fact that he was with his consituents at the time, there was another element at work in Boise: Church's credibility.

On July 17, relying on the experts, Church said there was no problem with Cuba. On Aug. 30 the picture changed -- he was called in Boise with the new information and told that he might be reading about it in the newspapers in a day or two.

On this business of Soviets in Cuba, Church had been there before. In 1962, relying on the experts, he told Idahoans there were no Soviet offensive missiles in Cuba. Church's newsletter reached Idaho the day President Kennedy went on television to say just the opposite.

"i did not intend to be 'had' again," he said in an interview. "I don't suggest it was anyone's intention that I be 'had.' But they anticipated the story would be leaked within 24 to 48 hours. I felt then that this was not the way. I couldn't let this happen to me twice."

"I'm bitterly criticized on the assumption that I have jeopardized SALT in a craven political way to appease my constituents," he said. "When you get out of step in this town, you become a lightning rod for all sides."

"most people around here accept that he jumped becaused of his political situation. They're aghast that he left himself so open," said a moderate Senate Democrat.

Senate Republicans, at least the far-right element that considers Church a plague on mankind, are rubbing their hands in glee. "They consider him arrogant -- that he got himself into this bind and he deserves it," one said.

One of Church's old political buddies back in Idaho said, "I thought he overreached. It was political, when he called a nighttime press conference on 'a matter of national security.' It is becoming more and more the perception out here that it was blatantly political."

Here is Church on Church:

"I know what they're saying, and I'm sorry there's this juxtaposition of SALT and Cuba with my campaign. People want to believe the worst. But I didn't put the brigade in Cuba. I didn't create the problem in the Senate for SALT. It stemmed from the brigade. This was not Angola or Afghanistan -- it was Cuba."

He went on, "2 regret it was linked, but from that point on, the real question was this: how can we deal with this in the Senate in a way that is satisfactory to the Senate and that will allow us to get the two-thirds votes we need to ratify the treaty? All the rest is political blather. Cheap shots."

Survival, obiously is understood by church. He is the only Democratic senator ever reelected from Idaho, managing somehow to live down his Washington reputation as a liberal by being uniquely Idahoan on issues of importance to his state.

He is, for example, always out front on legislation to help the sugar beet growers in idaho get higher prices. He is a darling of the nuclear industry, using his senate clout to funnel enormous grants to the federal atomic facilities in his state (7,000 Idahoans work in that industry).

"Unrelenting" is how his official biography describes Church's opposition to federal gun controls, a position that has always mystified eastern cynics.

Notwithstanding positions that are popular in a state as conservative as Idaho (it was big for right-wingers Lester Maddox in 1976 and John Schmitz in 1972 presidential votes), Frank Church is in a heap of trouble this time around.

His staunch advocacy of the Panama Canal treaties is haunting him, and the well-heeled national conservative campaign movement has made him a major target for 1980.

Church's likely opponent, although unannounced, is Rep. Steve Symms, a young Republican who is one of the more conservative members of the House.

The election is 15 months aways, but the campaign already is at fever intensity, Church's election team working intensely on telephone polls and voter lists, the opposition blasting away at him with radio and TV ads and brochures.

If it is feverish, it is also nasty, but probably not any worse than his 1963 race when Church was a leading opponent of the war in Vietnam.

"I've been throug it," he said, "and it was a lonely road for a long, long time. . . . Looking back, I think I was right about the war. I think I was right about the Panama Canal -- it was necessary for the country and its future."

This time, Panama is his albatross, and the heat is on. "I have a feeling that about this time in 1967, I was in worse shape by far. In Idaho, you don't oppose a war -- it's like pulling down the flag.I was down for the nine-count," he said.

He won, but this time, there are more groups punching away at Church. Targeting him for defeat are groups as varied as Stop the Baby Killers and the Idaho Right to Life Society; the Anyone But Church (ABC) Project of the National Conservative Political Action Committee, and a home-grown Committee for Positive Change.

"Of all the candidates to come along in recent years, Steve [symms] has got the clout and the nerve to take on Frank Church and beat him," said bill Clark, a farmer from Caldwell. "There's something about Symms. He never shows any fear. In the past, most ran against Church simply because someone had to do it."

Rancher Ted Landry amd another pont. "It doesn't matter if you are conservative or what in this state. You vote for the man and what he does."

Landry and thousands of other voters in Idaho, always a maverick, independent-thinking state, typically cast split ballots. That, experts say, is the only explanation for Church's popularity in a traditionally GOP fortress.

"Frank has done his homework here in Idago well and people remember that," said Boise businessman William Smith. "He may be a liberal on foreign policy but back here in Idaho we dont mind that. We just remember all the good things that Frank has done for this state. It really isn't tangible, but we just like the man."

Always a good speaker (he was a teen-age debating champ), Church is a particularly adroit one-on-one persuader -- a trait that runs counter to his Senate reputation of pomposity, arrogance and aloofness.

In recent months, even as he was floor-managing the canal treaties and talking favorably for SALT, he was also demonstrating for the home folks that he had not forgotten them.

In June, for example, he held up passage of an international sugar agreement while he argued for price-support legislation for his sugar beet farmers.

Lurking in the background, and sure tgo be an issue if Symms becomes Church's opponent, is a growing feud in Idaho over Middle East policy. Church is known for his pro-Israeli positions; Symms, Sen. James A. Mcclure, a Repulblican, and others are streidently pro-Libyan.

Libya is an issue because of Idaho farmers' attempts to sell grain there. Trade delegations have been exchanged. Church's opposition to the delivery of U.S. transport planes to Libya has caused a furor, and his opposition to last year's arms package deal for Israel, Saudi Arabia and Egypt -- even after the Carter administration changed its terms to suit him -fanned the flames.

"it is going to get brutal", said a church ally in Boise. "It is easy for the conservatives to put Frank on a hit-list, because campaigns are inexpensive here. But wer are looking at a $1 million campaign this time. Any other time, less than $500,000 would be a solid budget in Idaho."

Out-of-state money is pouring into Idaho for both sides, with the national conservative PAC, as an example, planning to spend $50,000 this year to chop away at PAC, as an example, planning to spend $50,000 this year to chop away at PAC, as an example, planning to spend $50,000 this

ABC director Don Todd in Boise said the issure basically is that Church is out of step with Idaho. "He runs as a conservative here, but he's liberal back there in Washington," Todd said. "every time he opens his mouth he creates a new issue for us. . . . He is a frightening man at this time."

Even though Todd and other Church foes maintain that the senator is running scared, many Idaho voters have shown in angry letters to newspapers that the tactics of some of the half-dozen action committees seeking to unseat him may be backfiring and helping Church.

Roger Whittaker, a farmer at Nampa, commented: "I still like Frank Church, even though I'm going to vote for reagan. He may look a little silly in Washington because of his switch on SALT, but we don't read Doonesbury here. We just remember what Frank has done for Idaho over the years."