LISBON, FEB. 3 -- Portugal agreed today to open talks with the United States on increased compensation for use of Lajes Air Base in the Azores without immediately calling for a formal review of the U.S.-Portuguese base accord.

The decision, announced by Defense Minister Eurico de Melo after talks with Defense Secretary Frank C. Carlucci, was seen as a gesture of patience by Prime Minister Anibal Cavaco Silva at the outset of what his aides expect will be drawn-out talks on faltering U.S. aid levels.

According to the 1983 base agreement, Portugal may demand a review any time beginning Thursday. The possibility of such a demand, will remain suspended over the talks as they progress, giving Cavaco Silva a negotiating card in reserve to back his insistence on guaranteed compensation.

De Melo cited Carlucci's long association with Portugal, saying the disagreement should be resolved "among friends." Carlucci was ambassador here from 1975 to 1978, a crucial period in Portugal's transition from dictatorship to democracy.

Portugal's willingness to postpone any demand for a formal review, which some U.S. diplomats had not expected, marked a clear gain for Carlucci. The Reagan administration, which only two weeks ago was forced to accept withdrawal of a fighter wing from Spain, has been eager to prevent an impression of further uncertainty over U.S. bases elsewhere.

Carlucci was to fly to Rome Thursday to pursue a "dialogue" on the possibility of redeploying to Italy the 72 F16s to be removed from Spain. He told reporters today that Washington has made no formal request to station the jets in Italy.

The Portuguese demand for more U.S. aid, unlike the Spanish stance, does not reflect political opposition to Lajes Air Base, officials here explained. But Portuguese officials have accused the Reagan administration of reneging on the spirit of the base agreement by reducing U.S. aid.

From $207.9 million in fiscal 1985, the first year the agreement was in effect, U.S. aid to Portugal fell each year to $117 million this year. Portuguese officials said they believed when the lease renewal was negotiated that U.S. aid would rise to the $207.9 million-dollar level and remain approximately there.

U.S. diplomats pointed out that the administration has sought higher amounts, only to have them cut back by Congress. Carlucci today called the congressional cuts "unwise," but U.S. officials said the administration was committed only to making its best efforts to keep the aid levels.