LISBON, FEB. 2 -- Frustrated by declining U.S. aid, Prime Minister Anibal Cavaco Silva has decided to seek a clear guarantee of increased and sustained payments for continued use of a strategic U.S. air base in the Azores, Portuguese officials said.

Defense Secretary Frank C. Carlucci is to hold talks with Cavaco here Wednesday, one day before Portugal is entitled to demand a review of the 1983 defense agreement renewing a lease on the facility. Diplomatic sources said the Portuguese leader plans to go ahead with renegotiation to obtain guaranteed aid levels, unless Carlucci has an acceptable alternative. The sources said that was unlikely.

The trouble over Lajes Air Base, which lies amid vital transatlantic sea and air routes 1,000 miles off mainland Portugal, comes only two weeks after the Reagan administration was forced to agree to withdraw 72 F16 aircraft from Torrejon Air Base in neighboring Spain. Similar questions have come on the horizon over U.S. bases in Greece, Turkey and the Philippines.

Prospects for Carlucci's mission in Lisbon darkened considerably with Friday's announcement that U.S. aid to Portugal, instead of being increased as demanded, is being cut back by another $30 million. From $147 million last fiscal year, aid to Portugal declined to $117 million for the 1988 fiscal year that began last October, the State Department said in Washington.

"This is not good news for the negotiations," a Portuguese official observed.

Cavaco, speaking to reporters after a meeting yesterday with President Mario Soares, said that in talks with the United States he will "defend with great force what we consider to be the correct position of our country."

The latest cutback intensified an impression here that Portugal is being taken for granted because its record as a NATO ally and its return to functioning democracy have taken it off the crisis list in Washington. This impression also was heightened by the absence of a U.S. ambassador from December 1986, when Frank Shakespeare left, until last Friday, when Edward Rowell presented his credentials.

"We feel the United States always reacts to a threat, and since we are no longer a threat, we have moved to second priority," an official complained.

Portuguese officials said the 1983 defense accord included a pledge by the United States to increase and then to maintain aid to Portugal in return for use of the base. In the first year, aid jumped as promised, from $147.9 million to $207.9 million in 1985. This created a benchmark by which the government in Lisbon has measured subsequent years.

With congressionally imposed cutbacks, the aid level fell to $188.9 million in 1986, then again to $147.4 million in 1987. The recurrent declines, Portuguese officials said, amount to reneging on the agreement.

U.S. diplomats here countered that the administration sought more than was granted each year but was forced by Congress to accept the lower levels. Reflecting frustration over the cuts, the State Department spokesman said Friday's reductions "pose serious risks to our foreign policy and national security interests."

In addition, a U.S. official pointed out, the 1983 defense agreement committed the administration to do its best to raise and then maintain the amount of aid, but contained no specific promise of a certain amount each year. This is the major change Cavaco plans to seek in the expected renegotiations, Portuguese and U.S. officials said. But only Congress can appropriate funds and it makes no commitments for future budgets.

Portuguese officials stressed that Cavaco's demand for increased aid payments in return for use of Lajes does not mean he wants to annul the agreement. In contrast to Spain, where demands for withdrawal of the F16s were political, Portugal has no desire to see the base abandoned, they said.

"The problem is not to discuss the agreement, but it is to get the United States to honor its promises in the agreement," a Portuguese official said. "Lajes is also good for Portugal. We realize this. We have no pressure from public opinion to ask for the impossible."

At the same time, Cavaco's government has refused to accept the argument that the State Department did its best, as promised, only to be thwarted by Congress. The 1983 accord, which runs until 1991, was a government-to-government bargain, binding both executives, an official insisted. "We think it's not enough to say it's a problem with Congress," he added.