Most Americans side with Congress in its clash with President Reagan over the proposed 1983 budget, according to a new Washington Post-ABC News nationwide opinion poll conducted shortly before the breakoff in talks between the president and leaders of the Senate and House.

By 59 to 28 percent, those interviewed said they want Congress to make substantial changes in Reagan's proposals rather than accept them without much change. The finding was virtually the same as one made in a mid-March Post-ABC News poll.

By 58 to 35 percent in the new poll, those interviewed want Reagan to drop his call for cuts in domestic social spending and cuts in taxes, and to try another program. Those figures also are similar to findings a month ago.

At the same time, however, the poll suggests that a continued impasse between Reagan and Congress could be at least as damaging politically to members of Congress as to the president. Among the 1,521 people interviewed in the poll, 43 percent said Congress would be more to blame than Reagan if they fail to reach agreement. Thirty-eight percent said Reagan would be more to blame.

The poll was conducted from April 21 through last Sunday, a period in which White House aides and congressional leaders were discussing possible compromises.

For the first time in a Post-ABC News poll, a majority--56 percent--said Reagan is going too far in cutting or eliminating social programs. Forty percent said Reagan's cuts in domestic social programs were about right or that he wasn't going far enough.

The poll also showed Reagan holding steady in popularity. Fifty-one percent said they approve of his handling of the presidency; 44 percent said they disapprove. The previous Post-ABC News poll showed 50 percent approval and 46 percent disapproval of Reagan. Over a six-month period before that, Reagan's approval rating suffered a steady decline.