White House chief of staff Donald T. Regan said yesterday that President Reagan would compromise with Senate Republicans on defense spending by cutting Pentagon waste or "stretching out" procurement of such things as munitions, food and fuel.

Regan, interviewed on NBC-TV's "Meet the Press," was asked where Reagan would be willing to compromise on defense in light of his demand Saturday that "vital weapons systems, either conventional or strategic, must not be touched, period" in any budget agreement.

"When we start talking about compromise on defense, let's remember, we're not going to compromise on security," Regan said. "Once we get beyond security, if there are methods by which we can achieve savings, either through elimination of waste or by stretching out a few things that are not necessary to our strategic or conventional weapons -- perhaps we can cut back somewhat on that spending."

Regan did not say what he meant by "security," again leaving open the question of what kind of compromise the president is willing to strike with Senate Republicans.

The Senate Budget Committee has approved a plan giving the Pentagon no spending increase beyond inflation, and GOP leaders warned the White House last week that the president risks getting less if he continues to balk at compromise. The Senate plan almost certainly would affect the major weapons systems that Reagan said "must not be touched, period," but details have not been worked out.

Having suffered one loss in the GOP-controlled Budget Committee, the president agreed last week to begin negotiations with Senate Republicans aimed at compromise. Regan and Senate Majority Leader Robert J. Dole (R-Kan.) will lead the talks, which are expected to begin this week.

When asked which weapons systems are open to compromise, Regan said: "I'm not sure I can be that specific . . . . It depends on what you mean by a weapons system. Do you mean the new pistol? Do you mean the new rifle?" Regan said that the president "was referring to the strategic weapons systems which he deems vital to the defense of this country."

However, the president and his aides have not said which weapons are "vital." Strategic weapons carry nuclear arms; conventional weapons are non-nuclear.

Pressed as to which areas are open to compromise, Regan said, "Many areas . . . . Munitions, food, oil. Many things where you can stretch out where your buildup is. I rely on Defense Secretary Cap Weinberger. He has assured me that if we have to do any compromising that he can figure out how to do this best and still carry out the president's mandate, so I'm relying on him to do that."

In past compromises with Congress, the White House has repeatedly agreed to defense savings that did not come from weapons programs but from lower inflation estimates and fuel costs.

Regan said the president "won't even touch" a one-year delay in Social Security cost-of-living increases, which the Senate budget panel approved, unless brought to him by bipartisan majorities of both houses.

Regan expressed doubt whether the 2.1 percent economic growth reported in a preliminary estimate last week would be sufficient to reduce the deficit. "I don't think we can grow out of the deficit problem," he said, but economic growth "will help" when combined with spending cuts.

The White House still wants to trim $50 billion from next year's deficit, he said.

Regan also said the MX missile vote in the House this week is "very, very close" and has tightened because the House leadership has begun lobbying against the missile.

The chief of staff also said former labor secretary Raymond J. Donovan could get a "suitable place" in the administration if he is acquitted of charges of grand larceny and fraud in a New York court.