The Soviet combat brigade in Cuba, subject of a month-long controversy between Washington and Moscow last fall, has resumed field maneuvers on the Caribbean island, the State Department announced last night.

The 6 p.m. announcement and background briefing for reporters preceded publication of the new intelligence about the brigade in today's National Intelligence Digest, and appeared to be a bid to head off leaks from this highly classified document in an election year.

The Carter administration, making public the existence of the Soviet unit last fall, initially declared that "the status quo" was "unacceptable" to the United States. After the Kremlin refused to remove the force, President Carter announced a series of U.S. countermeasures which he claimed had altered "the status quo."

Last night's State Department announcement said, "There is no change in our assessment of the character or size of the brigade. Although this is the first exercise of this size we have seen since last August, it generally fits the pattern by which the Soviets have exercised the brigade in the past." f

The Soviet unit, estimated to be 2,500 to 3,000 men with tanks, artillery and other field equipment, is not, in its current size and configuration, considered a physical threat to the United States. The State Department restated earlier this week, and reiterated last night, that the United States has "no evidence to suggest the presence of nuclear weapons anywhere in Cuba." h

An official said the present maneuvers, which are still under way, appear to be "almost a duplicate" of the activity that had been spotted at a training area south of Havana last August. That sighting by a U.S. reconnaissance satellite was taken as final confirmation of the theory that the Soviets had an operational unit, rather than a mere training or advisory force, in Cuba.

The State Department official, who did not permit use of his name under "background" rules, said Soviet training typically calls for field maneuvers every six months. He thus suggested that the reappearance of training activity just six months since it last was seen is part of an expected pattern. a

"The presence of the Soviet brigade in Cuba remains a source of serious concern to us," the official announcement said. It added:

"However, based on present evidence, this exercise in and of itself does not contradict our understanding that the Soviets will not enlarge the unit or give it additional capabilities."

Reporters were told that the United States is taking up the brigade activity with the Soviet Union through diplomatic channels. An official would not say whether the matter had been discussed by Secretary of State Cyrus R. Vance in his meeting yesterday morning with Soviet Ambassador Anatoliy F. Dobrynin.

Asked why the maneuvers are being publicly announced at this time, an official said that top-secret designations and other secrecy classifications mean nothing in present-day Washington, and therefore the information would soon be made public anyway.

The State Department announcement, in this light, was an attempt to forestall the kind of explosive political controversy touched off by the original disclosure last fall by electioneering Democratic Sens. Frank Church (Idaho) and Richard Stone (Fla.).

Church, in a statement telephoned to news organizations last night, termed the renewed maneuvers the Soviet Union's way of "flouting" the combat unit in the face of the United States.

The current disclosure takes place in a radically changed context of Soviet-American relations. Last fall the administration was striving to gain Senate ratification of the U.S.-Soviet strategic arms limitation treaty (SALT II). At that time, President Carter sought to minimize the tension with Moscow, saying Oct. 1 that "I have concluded that the brigade issue is certainly no reason for a return to the Cold War."