Most voters in the congressional elections across the country are rejecting President Reagan's attempts to pin the blame for the nation's troubled economy almost exclusively on former president Jimmy Carter and the Democratic Party, according to a Washington Post-ABC News poll.

Instead, voters are finding plenty of blame to go around for everyone: Carter and the Democrats, yes, but Reagan and the Republicans as well, and to virtually the same degree.

The question is not which party and president are to blame -- both are, in the public's view. The question, rather, is which side is more to blame. How individual citizens answer that, the poll shows, is a powerful indicator of their stated voting plans for Nov. 2.

Through the time of the poll, Oct. 4-11, Democrats were winning the battle of the blame and held a 60-to-40 point lead nationwide in the voters' general, overall congressional preference. Since then, Reagan has focused on the issue almost every day, launching bitter barbs at Carter and the Democrats.

Over the weekend, Reagan and House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) traded charges in national radio broadcasts, with the president defending his program and O'Neill saying it "is not working because the program is not fair . . .and because the people themselves know it is not fair."

Last week, Reagan, speaking in Omaha, said, "Our critics are saying our economy is on its knees. Well, you know something, if the economy is back on its knees, that's quite an improvement because two years ago it was flat on its back."

Conceivably, with the unique attention a president draws, Reagan may succeed in altering the public perception. Whether or not he does, however, the poll results show strikingly why the president and the candidates are spending so much time making harsh accusations about the past:

Thirty-six percent of likely voters blame Carter and the Democrats more than Reagan and the Republicans for the state of the economy, and they are lining up 3 to 1 behind Republican candidates.

But virtually the same proportion--34 percent, according to the poll -- blame Reagan and the Republicans most and are backing Democrats in congressional races by a 10-to-1 ratio.

The rest, 30 percent of the likely voters, blame Democrats and Republicans equally, according to the poll, and are splitting almost 2 to 1 toward Democratic candidates.

Such figures make clear the problem for Republican candidates and offer an explanation for the president's constant hammering at Democrats. Politically, the Republicans apparently need to do more than maintain that Reagan's program will work in the long run, the poll strongly suggests. They must pin the blame on the donkey.

They must win over independent voters with weak, if any, ties to either party and who follow politics less than more partisan voters and therefore may be more susceptible to 11th-hour persuasion. Independents will probably make up 25 to 30 percent of the electorate, a huge swing group with the power to determine the outcome in almost any election.

Success among such voters is necessary if the president is to maintain his "working majority" in the House. In recent months, however, independents, many of them concerned over high unemployment and increasingly dissatisfied with Reagan's handling of the economy, have been moving toward the Democrats, Post-ABC News polls show.

Nevertheless, success with independents on the "blame" issue may not be out of reach for the Republicans whose goal is only to hold their losses down.

While the total population assigns blame almost evenly to Carter and Reagan, independents do not. Fifty percent of them blame Carter "a great deal" or "a fair amount" for current economic conditions, one-third more than assign such blame to Reagan.

In all, 1,601 people were interviewed by telephone nationwide in the survey, including 855 who may be considered likely voters according to their statements about past voting and intentions this time.

Likely voters and the population at large fix only part of the blame for the recession on presidents and their parties. In the public's eye, the main culprits are not politicians, as far as the poll could determine, but rather foreign oil prices and big business, followed by labor unions and Japanese competition.

But none of them runs for office.