You're Sen. Frank Church of Idaho. You've been in the Senate since 1957. You were one of the most prominent Senate opponents of the Vietnam War. You ran a belated campaign for the Democratic presidential nomination in 1976 and beat Jimmy Carter head-to-head in four primaries. You helped steer the Panama Canal treaties through the Senate and you were an early backer of the SALT II treaty. This year, at the Relatively early age of 54, you finally became chairman of the prestigious Foreign Relations Committee. With any luck, you've got three more terms in the Senate, long enough to make the historians forget William Fulbright.

But, you've got this problem -- you're up for reelection next year and the voters of Idaho don't seem very impressed by your glittering Washington credentials. Five liberal democratic senators went down to defeat last year, and the republicans are even talking about taking control of the Senate after 1980. You've been targeted for defeat by right-wing groups and the Senate Republican Campaign Committee. The Panama Canal treaties are an issue that won't fade away. A group called the National Conservative Political Action Committee was showing spots on Idaho television that featured pictures of empty Titan missile silos and a voice-over that claimed you stood in the way of a strong defense.

You've already trimed your sails, but it didn't seem to help. You've always opposed gun control and supported prayer in the schools. Last year you voted against extension of the ratification period for the Equal Rights Amendment. Recently you broke new ground by voting against two liberal judicial nominees, Pat Wald and Abner Mikva, because of their support of gun control, and, in the case of Wald, her "anti-family views." But the polls still show that you are vulnerable.

It's late August and you're back in Idaho when you get a phone call from Under Secretary of State David Newsome informing you that the Carter administration has just confirmed the existence of a Soviet combat brigade in Cuba and that the story should be leaking out in the next 24 hours. You hang up the phone and have three choices:

1)Say nothing about the phone call and, when the story breaks, express mild concern and hold some desultory hearings of the Foreign Relations Committee. Remind yourself that this is what Bill Fulbright would have done.

2)Immediately announce in Idaho that there are indeed Soviet troops in Cuba -- after all, you're up for reelection. Maintain a calm tone by suggesting that this is a subject for negotiation with the Soviet Union and that, after all, we have troops on the borders of Russia. When asked about SALT, stress that this is a separate issue and that you oppose "linkage." Remind youself that this is consistent with your liberal record and what you said after your own trip to Cuba in 1977.

3)Make the announcement in Idaho as dramatic as possible and couple it with a hawkish proclamation that President Carter "should call for the immediate withdrawal of all Soviet troops from Cuba." Make certain the press picks up the significance of your observation that SALT cannot pass the Senate unless the Soviet troops are withdrawn. Remind yourself that Bill Fulbright was defeated and that reelection is the first rule of politics.

Back to reality. We all know that Frank Church chose the most expedient course and that Cuba has been in the headlines since then, as the SALT treaty twists slowly, slowly in the wind. Church is merely the most conspicuous of the 22 Democratic senators, mostly Northern liberals, facing reelection next year. (Two others have announced their retirement from the Senate). Senate Democrats are a nervous breed. For example, moderate Fritz Hollings of South Caroina declares, "Ain't nobody going to run to the right of Fritz Hollings this year." Only John Culver of Iowa is making a fetish out of his fidelity to liberal principle. In fact, Culver is hanging so tough that his campaign song might as well be, "You Can Take This Job and Shove It." But even Culver admits he has problems, telling a campaign audience this summer, "I've been targeted by so many people that I feel like Gary Gilmore."

The word "targeted," as awkward as it may sound, is a useful image for the plight of Senate liberals. Imagine a hardy band of them trapped in a forest and surrounded by conservative yeomen with arrows marked "abortion," "school prayer," "ERA," the Panama Canal" and "balance the budget." The liberals could follow the lead of Frank Church and run directly toward the archers shouting, "Don't shoot, I'm really one of you." Or they could all line up behind John Culver as he bellows, "I can lick any man in this forest. Do I take you on one at a time or together?"

Luckily for the reelection prospects of most Democratic senators, there is a third possibility. And that is to take cover wherever you can find it.

Some, like Gary Hart of Colorado, are well entrenched behind fortifications they have been constructing from the day they arrived in the Senate. Others, like George McGovern of South Dakota, are merely backing up a few steps, convinced their very prominence provides a measure of security.

Running for cover is as much a part of politics as an orderly retreat is a part of military strategy. It is practiced by politicans of all philosophies who find themselves in trouble with the voters. Last year among incumbent senators, it was two Republicans, Strom Thurmond and Chuck Percy, who came up with the most inventive ways of running for cover.

As a public service for politicians of all parties, what follows is a nine-step guide designed to help you run for cover successfully. It is tailored to the needs of Senate Democrats because they are the ones who need protective covering the most as 1980 approaches. Although there are no guarantees, and life is known to be unfair, any incumbent who follows at least six of these rules should win in a landslide -- barring an election eve indictment.

If political principles matter to you, and you don't mind having your family and supporters sit up until 4 a.m. watching the seesawing returns, you should be able to squeak through by following just three rules. But ignoring this primer entirely, or abiding by just one or two rules, is an almost certain ticket to a law firm or a foundation task force come 1981.