No section of the country, including South, has accumulated more clout in Congress than the Pacific Northwest. But this year the congressional giants from Oregon, Washington and Idaho are all hard pressed to win reelection.

For the Pacific Coast is receding from the national capital, and its drift spells immediate trouble for Jimmy Carter in the election, and long-term difficulty for the harmonization of regional differences in the country as a whole.

Congressional strength tends to accrue to regions with a case against the national majority. The South entrenched itself in the congressional committees as a defensive measure against industrialization and desegregation by Republican presidents from the North. The Pacific Northwest has been the last frontier. Its political problem has been springing the vast energy potential required for development without rape by the private interests more dominant in the national scheme of things.

To that end, an institutional balance between public and private power was struck some 50 years ago with the federal government. The Grand Coulee and Bonneville dams on the Columbia River are monuments to that bargain. So are the vast nuclear power installations at Hanford to flourish in this state. a

Irrigation from those projects caused agriculture to flourish in western Idaho and the eastern parts of Washington and Oregon. Cheap power fostered industry in all three states. During the last part of the past decade, self-sustained growth set in, the region took off and, as population swelled, real estate boomed. Idaho, as a result, has the highest per capita number of millionaires of any state in the union.

The architects of the program that fostered that growth are mainly Democrats who cut large figures in the national capital. But not with the voters here at home. Difficult campaigns confront all of the following incumbents:

Warren Magnuson of Washington, the senior member of the Senate and chairman of the Appropriations Committee who has dispensed billions in this state, including almost a billion dollars for the Mt. St. Helens disaster.

Frank Church of Idaho, a senator since 1956, chairman of the Foreign Relations Committee and No. 2 (after Henry Jackson of Washington) on the Energy and Natural Resources Committee.

Tom Foley of Spokane, Wash., chairman of the House Agriculture Committee and, as chairman of the Democratic Caucus in the House, the fourth-ranking member of the leadership there.

Mike McCormack, congressman from Richland in the Columbia Valley and a member of the Public Works and Science and Technology committees. At one point his district alone received, for the big dams, 20 percent of the total national budget for public works.

Al Ullman, congressman since 1956 from the Second District in Oregon and chairman of the Ways and Means Committee, which deals with taxes, Social Security, health insurance and welfare.

Slightly different reasons explain why each man is in trouble. Sen. Magnuson, for example, is 75 and looks it. Sen. Church is said to be too liberal for his increasingly conservative state.

But underlying the difference in each case there is a single, overwhelming reality. This area has moved beyond dependence on the federal government. It is well off economically and is filling up with new people oblivious of the struggles of the past. They are impatient with federal restrictions, and many want to slow development for environmental reasons.

The most popular Democratic candidate here. in Washington is Jim McDermott, a child psychiatrist from Chicago, who is running for governor. Last month McDermott, a strong environmentalist, became the first challenger to beat an incumbent governor in a primary in Washington since 1908. He upset Dixy Lee Ray, a former chairman of the Nuclear Regulatory Commission and a proponent of atomic power.

Polls show McDermott currently leading his Republican opponent -- John Spellman -- by upward of 20 points. All the other candidates here are looking to him for help. What he says of Sen. Magnuson expressed the difficulty all experience.

"Many people here are newcomers. They're willing to take chances on the future. They don't know what Magnuson did for them in years past. They want to know what he's doing today."

Though Sen. Magnuson and Rep. Ullman seem particularly hard pressed, it may be that they, and all the others, will pull it out. But there is no gainsaying the alienation of this part of the country from the national headquarters, in general, nor, in particular, the hostility to becoming the plaything of the country's energy problem.

That not only complicates developing national policies for energy, and the economy. It also works against President Carter. The Democrats had hoped to pull away votes that are now going to John Anderson, particularly in Oregon. Vice President Walter Mondale was in both Washington state and Oregon over the weekend on that task. But the job is apt to be much harder than imagined. A vote for Anderson is not a wasted vote for people who want to send the capital a message -- especially when the message is: keep out.