President Reagan began backing away yesterday from a controversial proposal to squeeze $40 billion in savings from the Social Security system that was included in a budget compromise with Senate Republicans and was unconditionally endorsed by Reagan last week.

Deputy White House press secretary Larry Speakes said Reagan hopes the full Senate will approve the compromise worked out last week with Republican leaders but will not insist that the Democrat-controlled House agree to identical budget proposals.

"If there are differences on Social Security between the two houses, then it will be worked out in conference," Speakes said.

"I think we will work with the House and let things develop over there and then work out the differences and then come out with a piece of legislation that will meet the approval of the majority of the House and Senate and something the president can sign," he said.

The White House, while trying to avoid offending Senate Budget Committee Chairman Pete V. Domenici (R-N.M.), who worked out the compromise, also clearly wanted to get out of the line of fire from Democrats.

They have had a field day painting Reagan as advocating cuts in Social Security benefits, while the president has tried to deny it.

The fancy footwork on Social Security was also a bow to political realities in the House, according to one aide.

"The House ain't going to buy" reductions in Social Security, he said.

Clear indication of that came Tuesday when House Minority Leader Robert H. Michel (R-Ill.) rejected proposed cuts in benefits and said he would not push for House passage of the compromise with Senate Republicans.

Last week, Michel, in a display of Republican unity, had stood with Reagan in the Rose Garden as the president announced his personal backing for the compromise.

"Politicians are believers that consistency is the hobgoblin of little minds," one White House aide said jokingly of Michel's turnaround, before adding understandingly that Michel had encountered broad opposition from GOP House members to reductions in Social Security as the campaign season warms up.

Earlier yesterday, Reagan had seemed to dismiss the uproar caused by Michel's comments, telling reporters, "You can't believe everything you read in the papers."

But presidential advisers took it seriously, although they were careful to say that they did not regard Michel's actions as disloyal or a defection from the ranks.

Office of Management and Budget Director David A. Stockman said GOP opposition in the House will force further changes in Reagan's budget, although he declined to predict whether the proposal for reducing Social Security by $40 billion over the next three years would be dropped from the revised budget.

Stockman, telling reporters "you don't put a budget together without accommodation and compromise," said the administration is working to "find 218 people to support a plan that's reasonably close" to Reagan's budget proposals. He was referring to the number of votes needed for House passage of a budget bill.

"The situation right now is that you've got a fractured House," another aide said. "We'll be moving hard in the Senate."

Meanwhile yesterday, Reagan held the second of three meetings with financial leaders to solicit their support for a budget compromise. The financiers, heads of major insurance companies, banks and Wall Street brokerage houses, said they told the president that interest rates would remain high until the administration and Congress agree to a plan for reducing budget deficits.

Robert H. B. Baldwin, president of the Morgan Stanley investment banking firm, said he prefers the Reagan-backed plan to one offered by the Democrats and plans to support it.

Arthur Levitt Jr., president of the American Stock Exchange, agreed.