President Reagan yesterday reaffirmed his intention to revise the U.S. proposal in strategic arms talks with Moscow and told his chief negotiator "to examine all Soviet proposals seriously and to be flexible in our responses wherever this would be consistent with our overall objectives."

After a 20-minute Oval Office meeting with Reagan, Ambassador Edward L. Rowny told reporters he was "confident that progress" can be made in the strategic arms reduction talks (START) if the Soviets bargain in good faith as he said the administration was doing.

The talks, aimed at curbing the long-range nuclear-tipped missiles of both sides, resume in Geneva on Wednesday. They began a year ago and have made little visible progress toward an agreement thus far.

Rowny said "the president's main objective" at yesterday's meeting "was to get my views on what changes he should make in my instructions."

In an all-out bid to win support from Democrats and moderate Republicans in Congress for deploying 100 new 10-warhead MX missiles, Reagan had pledged to alter the U.S. proposal to conform with recommendations of a special bipartisan commission that urged "the vigorous pursuit of arms control."

The commission also called for an eventual move away from multiple-warhead missiles toward less threatening single-warhead ones on both sides that would lessen the temptation to strike first in a crisis.

But how to change the U.S. START proposal to conform to these recommendations is a matter of dispute within the administration. The issue is especially sensitive because congressional moderates have warned the president that they could reverse themselves on the MX if the new proposals are less likely to lead to serious negotiations with Moscow than the current U.S. position.

Rowny, a retired general, did not say what changes he recommended to Reagan. But he is known to agree with the Pentagon and the new leadership of the U.S. Arms Control and Disarmament Agency who favor emphasizing sharp reductions to equal levels in the amount of lifting power, or throw-weight, in each side's missile arsenal.

The State Department, in general, opposes this. The Soviets, who traditionally have had much bigger missiles than the United States, have always had a big lead in this measurement of power. State Department experts believe that switching tactics and attempting to force the Soviets to make huge cuts and changes in their forces on such a basis now would lessen rather than improve chances for an agreement. In a speech in Detroit on Monday, Rowny put heavy emphasis on the throw-weight issue, claiming that unless this is equalized the Soviets would retain an advantage that would allow quickly adding missile warheads if any future agreement is breached. The key questions on throw-weight, on changing or eliminating limits on the numbers of missiles allowed each side under the existing U.S. proposal, and on what, if anything, to do about jet-powered cruise missiles will be discussed and probably decided at a White House National Security Council meeting next week just before Rowny's return to Geneva.

Rowny also said Reagan will "continue to give serious study" to how to apply the concept of a so-called guaranteed "build-down" to the START proposal.

This is a concept introduced by Sens. Sam Nunn (D-Ga.) and William S. Cohen (R-Maine) that was endorsed in general terms by the special commission and by Reagan. It, too, is politically sensitive because moderates like the idea and have tied their support of MX to it. The concept requires removal of more than one atomic weapon from the arsenal every time a new one is added.

Several officials said it was not likely that this build-down scheme, which also has opposition within the administration, will be worked out in time for presentation in any revised START proposal this month. They said it will take at least several more weeks to come up with a formula that seems workable.

The president, however, made clear he was not backing away from this idea when asked about it by reporters at a separate picture-taking session.