President Reagan has decided to put off his scheduled endorsement of a new MX missile plan next week because it might complicate White House efforts to defeat the nuclear freeze resolution in the House, administration sources said yesterday.

These sources said that House Republican leaders had urged the White House to postpone any statement on the MX until the freeze resolution comes up for vote on the floor Wednesday.

The President's Commission on Strategic Forces will issue its report as scheduled Monday, calling for deployment of 100 MX intercontinental ballistic missiles in existing Minuteman silos, engineering development of a smaller future missile weighing about 15 tons, continued deployment of the Trident II submarine-based missile and research on anti-ballistic missile defense.

Reagan had intended to issue a prompt endorsement the following day, in concert with members of Congress of both parties who support the MX.

But House leaders told White House chief of legislative liaison Kenneth M. Duberstein and chief of staff James A. Baker III that presidential efforts to push the controversial MX on the eve of the nuclear freeze vote would be harmful, administration sources said.

On the recommendation of aides, Reagan then decided to put off his statement for a week, until April 19. This will leave time for the freeze vote and the scheduled Senate vote Thursday on the nomination of Kenneth L. Adelman to be director of the Arms Control and Disarmament Agency, officials said. That, too, is controversial.

However, the delay also will offer an opportunity for officials in the administration and the White House who are opposed to the commission's proposals to have yet another chance to change them.

The report has been constructed carefully as a compromise, and among other things is said to have the support of all three living former presidents, Richard M. Nixon, Gerald R. Ford and Jimmy Carter.

But it moves away from a number of past administration positions and is likely to provoke objections both from those opposed to any MX and those who think the deployment recommendations do not go far enough.

The commission unanimously endorsed the proposal for deployment of 100 MX missiles. But Brent Scowcroft, the commission chairman, is said to believe that Congress will approve a lower number, while there were those on the commission who argued strongly for eventual deployment of 200 missiles.

Sources said that those who favor the higher number will use the interim provided by the president's delay of an endorsement to recommend production and deployment of an additional 100 MX missiles later if the Soviets do not agree also to switch in the future to smaller, single-warhead missiles instead of the large multi-warhead ICBMs they are deploying now.

The commission recommends that a smaller U.S. missile, weighing less than a sixth as much as the 100-ton MX, go into development and production by the late 1980s.

The commission recommendation looks to the small missile rather than the MX as the basic future land-based ICBM in the U.S. arsenal.

The commission's plan also is certain to come under attack from liberal Democratic critics who are opposed to MX deployment.

In a speech at American University yesterday, Sen. Edward M. Kennedy (D-Mass.) sarcastically attacked the commission proposal to put the MX in what he called "old, vulnerable Minuteman silos."

This, he said, is "like having a car that is getting wet because of a leaky garage roof, and trying to solve the problem by changing the make of the car."

"It is time to make it clear that even by the administration's own logic, the MX in the Minuteman silos is a sitting duck, and to state clearly that, by any rational standard, the MX missile in any form is a dead duck," Kennedy said. Another sign of impending opposition came in a letter from a dozen House Democrats, including Rep. Joseph A. Addabbo (D-N.Y), chairman of the House Appropriations defense subcommittee, which made one of its criteria for support deploying the MX in a way that would deter rather than encourage a Soviet first strike.

Putting MX missiles in Minuteman silos has been criticized on Capitol Hill as encouraging a first strike.