Regardless of how the most recent national intelligence estimates on the Soviet threat are interpreted, a broadened constituency favoring higher defense spending faces the Carter administration, according to Pentagon leaders.

This promises to make 1977 a repeat of 1976 when Congress gave the Pentagon virtually all the money it wanted for a military force of 2.1 million service people armed with new generations of weapons.

Defense Secretary Donald H. Rumsfeld said in an interview that the constituency was broadened as the information the Pentagon put out on the Soviet military buildup got through to Americans and their representatives in Congress.

"It has not been so much a revelation" that the Pentagon suddenly made about the buildup, Rumsfeld said, "but a water treatment" of repeating the facts over and over until they penetrated the public consciousness.

While agreeing with that observation, the Pentagon executive in charge of dealing with Congress - William K. Brehm, assistant secretary of defense for legislative affairs - said the new congressional budget committees also helped broaden the constituency for the defense budget.

Instead of the old procedure of members picking at little parts of the Pentagon budget sent to the House and Senate floors by the Armed Services and Appropriations committees, CONGRESS THIS YEAR FOR THE FIRST TIME "had to bite the bullet" and come up with its own figure on how much is enough for national defense, Brehm noted.

As it turned out, the House and Senate Budget committees set a ceiling of $112.1 billion in budget authority for the Pentagon for fiscal 1977, or almost the $13.3 billion requested. The fiscal year began Oct. 1.

"This was the first year they could not escape making some kind of decision" on how much was enough for national defense, Brehm said. "They had to make some kind of decision - stand up and be counted."

The new process had the additional benefit of shifting the congressional focus from nitpicking "what kind of guidance should be on the Sparrow missile" to such larger questions as "how NATO forces should be modernized," he said.

Brehm credited former Defense Secretary James R. Schlesinger with starting the turnaround in the attitude toward defense spending by attacking Congress and others who favored cutting the Pentagon budget.

After Schlesinger was fired by President Ford in November, 1975, with part of the reason being Schlesinger's refusal to support a military budget $6 billion lower than he favored, Rumsfeld went to the Pentagon. He made the case for higher defense budgets in softer but persistent pitches.

"When I came to the Pentagon 14 months ago," Rumsfeld said in an interview, "the facts" about the Soviet military buildup "were the same as they are today." The Soviet Union was going through a broad modernization program in missiles, aircraft, tanks, submarines, and ships.

Rumsfeld said he read the most recent national intelligence estimates about the Soviet buildup and found nothing new in them in the sense of any spectacular advances in weaponry.

The new intelligence report, the Defense Secretary said, "is very close to what I've been saying all year." What Rumsfeld said at his Sept. 27 news conference at the Pentagon typifies what he has been saying all year.

"The Soviet Union today is clearly militarily stronger and busier than in any other period of its history . . . The Soviets continue to press ahead with agressive development programs for both land-based ballistic missiles and submarines launched ballistic missiles.

"The scope of these programs is unprecedented, either in the Soviet Union or in the United States," Rumsfeld continued. "While recent developments were not unexpected, they nevertheless reinforce one's concern about the purposes behind their energetic activities."

Rumsfeld did not suggest the Soviets were out to achieve military superiority over the United States or blow up this country in a surprise strike.

"I didn't think it was necessary to talk about intentions," Rumsfeld said in an interview with The Post. However, other arms specialists, like former Deputy Defense Secretary Paul H. Nitze, shaped the iron Rumsfeld had heated by assigning dark intentions to the Russians.

Rumsfeld acknowledges that Russia's military modernization program is within the law, so to speak. He said: "We continue to expect that the Soviets will eventually deploy close to the 1,320 MIRV (multiple warhead) missiles permitted under the Vladivostok understanding assuming a SALT (strategic arms limitation talks) II agreement is reached."

Other Pentagon executives have gone beyond Rumsfeld's restrained statements, however, in sounding an alarm about the Soviet military buildup.

Said Malcolm R. Currie, the Pentagon's research director, on Feb. 26: Russia's technical advances in missiles "are only done for one reason, strategically, and that's to develop a countersilo capability. It's the only rational explanation . . . The Soviet Union has never accepted this theory of assured destruction" under which each side figures it would not be worth fighting a nuclear war because of the massive damage that would be inflicted by both sides. "They feel strategic war is kind of inevitable . . ."

On top of that scary rhetoric came the hawk vs. superhawk debate on national defense between President Ford and challenger Ronald Reagan during the Republican presidential primary campaign, plus public opinion polls indicating the American people wanted a stronger military.

Democratic political leaders advised their members in Congress last year to contain the defense budget debate to Ford vs. Reagan by going along with Ford's Pentagon budget request. While this amounted to only a temporary broadening of the constituency, the polls had a more lasting effect.

"Americans have become significantly more sympathetic toward overall military and defense spending," said Potomac Associates in discussing the results of its polling last year in a pamphlet. "The Pursuit of National Security: Defense and Military Balance."

Specifically, the Potomac Associates poll indicated a growing number of Americans wanted defense spending to go up, with 9 per cent of those surveyed in 1972 favoring an increase; 17 per cent in 1974 and 28 per cent in 1976. The percentage that wanted defense spending to be reduced dropped from 37 per cent in 1972 to 33 per cent in 1974 and 20 per cent in 1976.

Rumsfeld, stressing to Congress that the Soviet military buildup "is real and powerful" and would not be restrained if the United States failed to respond through higher defense spending, has cautioned against overreacting by throwing gobs of money at the problem.

The Pentagon's new defense budget calls for $123 billion for fiscal 1978 starting next Oct. 1, about $10 billion over the fiscal 1977 request but not a panic reaction in the view of defense leaders. The five-year budget plan Carter will inherit calls for a steady growth in defense spending in response to the Soviet buildup.

But partly because the "Russians are coming" rhetoric will be broadcast louder than ever this year by hawkish organizations aided by new interpretations in the Central Intelligence Agency's latest report on the Soviets, arms control groups fear defense spending will soon get out of hand.

"Apparently there is a major effort underway to recreate the atmosphere of the 'missile gap' days of 1960" when Democratic presidential candidate John F. Kennedy charged the Republican administration with letting the Soviet Union get way ahead of the United States in intercontinental ballistic missiles, said Thomas A. Halsted, executive director of the Arms Control Association.