October 15, 1986

Behind the high concrete-block walls that keep the Ilopango air base here from the public's view is a drab two-story building. Over the last three years, the building has served as the waiting room for agents working for the Central Intelligence Agency, leaders of the Nicaraguan rebels, mercenaries and American military advisers, according to American officials and Nicaraguan rebel sources. Now more than ever the base is the center of C.I.A.-supported operations to supply Nicaraguan rebel forces, according to an American shot down in a supply plane over Nicaragua. American men in civilian clothes often pass through the base's gates and American officials say privately that it is the center of C.I.A. and other clandestine operations here.

The new chairman and chief executive of the financially troubled BankAmerica Corporation, A. W. Clausen, said yesterday that a $2.8 billion takeover bid from First Interstate Bancorp of California would be rejected. Speaking before 200 of the bank's senior executives in a meeting for officers only, bank sources reported him as saying, in essence, ''I didn't come here to preside over the sale of BankAmerica to First Interstate.'' Joseph J. Pinola, chairman of First Interstate, did not return phone calls for comment but is understood to have received no word from the bank, official or otherwise, on his $18-a-share offer. One leading bank analyst argued that, while Mr. Clausen ''harbors the notion he can fix BankAmerica,'' this approach could be a bargaining ploy. ''Some of the bank's executives will tell you,'' he said, ''that the deal makes a lot of sense and the real issue is price.'' Mr. Clausen told the executives he might be willing to sell when the stock reached $35.

A radio announcer here this morning told of calling a friend, a young accessories designer, and finding her asleep at 10 o'clock last night. Why, he asked, was she in bed so early? Because of the bombs, she replied. Because the Americans are not coming and there is nothing to do.

President Reagan appealed to the Soviet Union today ''not to miss the opportunity'' for a major breakthrough on reducing nuclear weapons, saying such an agreement was ''within our grasp.'' The statement by Mr. Reagan marked the second straight day he has made such an appeal, and it came as he and the Soviet leader, Mikhail S. Gorbachev, engaged in a public competition to promote their own interpretations of the outcome of the meeting in Iceland. Mr. Reagan and other Administration officials undertook a major campaign to explain Mr. Reagan's decision to refuse to accept restraints on the development of a strategic defense system against nuclear weapons. Intermediate-Range Arms The White House also began an effort today to salvage something from the Iceland meeting by asserting that the issue of intermediate range missiles had been effectively resolved in Reykjavik despite the absence of a formal agreement.

Having heard the opinions of 1,000 people about Long Island, Prof. Elaine Sherman has arrived at this conclusion: ''We have an identity problem.'' Never mind that Nassau and Suffolk Counties have a combined population of 2.6 million, larger than 21 states. Never mind that the island has a booming and diverse economy with more affluent consumers than are found almost anywhere else in the country. Never mind that it can boast such internationally famous playgrounds as the Hamptons and Fire Island as well as an impressive list of museums, art galleries and other cultural attractions.