President Reagan said yesterday that the budget resolution passed by the Senate cuts more deeply into military spending than he would like but that he accepted it on condition he can return to Congress later for additional military spending.

Reagan also said he accepted a one-year delay in Social Security cost-of-living adjustments because "I was faced with a mandate" in the Senate for it.

Speaking to reporters in Lisbon before returning here from his 10-day European trip, Reagan again vowed to veto any tax increase. He said the Senate-passed budget gives him 90 percent of deficit savings he sought.

"It is easy for some to attack individual elements of the Senate package, but I'm convinced this was the only serious deficit reduction package that could pass the Senate," Reagan said in a statement after returning to the White House.

Noting that U.S. allies expressed concern about budget deficits at the economic summit in Bonn, Reagan added, "How sweet it is to return with a 50-49 Senate victory for spending restraint and no tax increase."

On defense, Reagan originally sought a 6 percent increase in spending authority after inflation. That was pared to 3 percent, and the Senate yesterday voted zero growth above inflation for next fiscal year and 3 percent in each of the next two years.

Reagan, who last week insisted that anything less than a 3 percent increase would be "irresponsible," said yesterday that he accepted zero growth because senators promised him that he could seek more money later if "national security" is affected.

"Not a penny more should be taken out of that budget than has been given now," he said in Lisbon. "And as I've said, we're talking about the year of 1986, and I have the agreement of the Senate that if this represents, and I, in my own mind feel that it does represent a cut in spending beyond which we should go, that they recognize that I will be returning for a supplemental appropriation."

White House chief of staff Donald T. Regan said the president telephoned Sens. Pete Wilson (R-Calif.) and Edward Zorinsky (D-Neb.) from Air Force One yesterday to thank them for their budget votes. Wilson voted from a wheelchair after being transported from Bethesda naval hospital where he underwent an appendectomy.

"The play now goes to the House," Regan said. "It's up to the House to come up with a budget. They're going to be challenged. They're going to have to come up with an alternative plan."

Regan predicted the Senate would "hang tough" against compromise.

On Social Security, the president had accepted a plan that would have guaranteed recipients a 2 percent cost-of-living adjustment (COLA) increase for three years and more if inflation exceeded 4 percent. This plan would have approximately halved the COLAs.

Instead, the Senate voted to freeze the COLA for one year, which produces about the same amount of deficit savings as the earlier Reagan plan.

Reagan promised in his reelection campaign not to reduce Social Security benefits and, in December, said the pledge applied specifically to inflation adjustments.

Yesterday he said that, during the campaign, "I didn't have in my mind that we were talking about potential or possible increases. But it was taken that way and so okay, I live with that."

In January, Reagan said the only way he would consider a COLA freeze would be if a bipartisan majority of the House and Senate presented him with a mandate. Yesterday, he seized on the Senate vote as that mandate.

". . . I would suggest that I was faced with a mandate when 79 percent of the Senate, which means pretty much half-and-half, Democrat and Republican -- demanded that we have some curbing of the COLAs," he said.

Reagan said his 2 percent plan was not well understood, particularly among Social Security recipients, even though White House surveys showed that 70 percent liked the idea when it was explained to them.

Asked whether he views the Social Security and defense aspects of the budget to be a "cave-in," Reagan said he does not.

"I have always believed from all my past experiences as a negotiator that you recognize that the other fellow probably is going to offer less than whatever you ask," he said. "And I've always kind of believed in leaving a cushion there for dealing. But, this time, things have changed.

"This was a deal; I don't like the word deal. This was a working out of a budget that was acceptable to the Senate as well as to ourselves . . . . I recognize in the give and take that must take place in a system such as ours to attain more than 90 percent of what we asked for means that all right we can, we can do some giving along the line also."