The House Republican Campaign Committee has launched an ambitious new policy of targeting vulnerable Democratic congressional districts two years ahead of time and financing prospective candidates considered likely to defeat the incumbents.

The $4 million the committee plans to spend for this purpose in 1977 is more than three times the committee budge in any previous non-election year.

It represents the convictions of House GOP leaders that the party is at a political crossroads and must make a comeback in 1978 to survive. It also reflects the realities of the federal campaign spending law, which limits expenditures during the campaign period.

"Campaigning for Congress is now in many respects a four-year effort," says Steven Stockmeyer, staff director of the GOP campaign committee. "Too often, in the past people have been willing to cast off candidates because they didn't win. But a number of Democrats who won in 1974 were trying for the second time."

It was with this conviction that the committee did survey research in 50 districts where the GOP candidate came within 5 percentage points of winning in 1976. They identified 20 candidates who seemed good bets to win if they could convinced to run again.

As a result, House Minority Leader John J. Rhodes (Ariz.) and campaign committee Chairman Guy Vander Jagt (Mich.) have telephoned and written these candidates, urging that they decide now to run in 1978.

"I want you to know that should you decide to give it another try, you can count on the full resources available to the Republican leadership," says a letter from Rhodes to these designed candidates. "For my part, I will participate actively in fund-raising for your campaign and am willing to go to work at once to help pay off whatever debts you may have incurred during the last campaign."

This approach represents a departure from past practice, when the GOP campaign committee stayed out of races until a candidate was chosen by the primaries. But the situation is now so critical that the House GOP leaders regard waiting for the 1978 primaries as a luxury they cannot afford.

The elements of the off-year campaign program include:

A major research effort to identify vulnerable incumbents and concentrate financial resources in these districts.

Creation of a field staff with the single function of identifying strong candidates and recruiting them to run.

Institutional television advertising in 25 media markets that reach vulnerable districts. The programs will include 60-second spots and half-hour programs and will be designed to express a positive Republican approach. The firm of Bailey & Deardourff, which managed Gerald Ford's media campaign, is being consulted in preparation of this advertising, which will be tested this summer for use late in the year or early in 1978.

A "bad news network" consisting of news releases that will provide negative aspects of a Democrat's record back home. When possible, the words of criticism will be put in the mouth of a GOP spokesman in the district.

Where the GOP campaign committee departs most from past concepts is in its identification of vulnerable incumbents. Traditionally, the notion of vulnerability has been based largely on registration statistics, which Stockmeyer says is outmoded.

Stockmeyer says that all of the committee's research shows that the voter perception of a congressman's district service is the singel most important element in his election.

This was partly the reason that the GOP campaign effort in 1976 was such a dud. It was based on the premise that the most vulnerable Democrats would be members of the large "Watergate" freshman class of 1974, when many Democrats won previously secure GOP congressional districts.

The GOP concentrated on these districts, ignoring the fact that most of the Democratic freshmen were going out of their way to give good constitutent service. As a result, the GOP beat only two freshman and one of these only because of a sex scandal.

"Now we're operating on the premiser that there are no safe districts, just safe incumbents," Stockmeyer says.

It is with this perception in mind that the campaign committee is throwing its resources into a special election Feb. 22 to fill the northwestern Minnesota district vacated by Secretary of Agriculture Bob Bergland.

Classically a swing district, the Minnesota 7th became a "sage" district when Bergland won in 1970, but Stockmeyer says he believes it was safe for Bergland, not the Democrat Party.

In sort of a preview of how the new targeting system might work, the GOP expects in next Tuesday's primary to come up with a tailor-made candidate: Lutheran farmer Arlan Strangeland, 46, in a district where research shows that more than 80 per cent of the people think that electing a farmer is "very important" or "absolutely necessary" and where more than 70 per cent of the electorate is Lutheran.

The GOP is running a $150,000 campaign for Strangeland, with more than half the money coming from outside the district and with resource supplied by the congressional campaign committee. Stockmeyer says he expects it to be a harbinger of campaigns to come.