September 20, 1986

President Corazon C. Aquino was triumphantly welcomed back yesterday to the city where she went to college, garnering tributes from Mayor Koch and drawing emotional cheers from enraptured New Yorkers. Mayor Koch, in presenting Mrs. Aquino with a key to the city, said: ''It will open our doors. You already have our hearts.'' Meanwhile, in an important development, a spokesman for Mrs. Aquino said last night that the 483 commercial banks to whom the Philippines owes $14 billion of its $26 billion foreign debt were ready to lower annual payments.

The House of Representatives today voted, 329 to 4, to strengthen the law protecting public health and the environment from chemical pesticides. If the legislation is passed by the Senate and signed by President Reagan, it would accelerate the retesting of more than 600 potentially dangerous chemicals in nearly 50,000 products. Under the law, pesticides include chemicals to control insects, weeds, rodents, fungi and other agricultural and household pests. Many of the pesticides now in use were registered as long ago as the 1940's, well before some of the dangers they represented were recognized. The Environmental Protection Agency has been retesting the pesticides as a prelude to reregistering them, but has been able to review only about 25 a year.

Representatives of major trading nations struck compromises on agriculture and the service industries early today, virtually assuring a new round of negotiations to strength the world economy through freer trade. The United States trade representative, Clayton K. Yeutter, predicted that final agreements would be reached early today. ''Basically we've accomplished a lot, but there's more to do,'' Mr. Yeutter said shortly after midnight as he rushed between negotiating sessions at this windy South Atlantic resort town. Eighth Round of Talks Delegates of the General Agreement on Tariffs and Trade are writing the guidelines for what will be the eighth round of trade liberalization talks since World War II. The actual negotiations are expected to last well into the next decade and set rules that would govern trade until 2000.

Spurred by the collision of a Mexican jetliner and a small plane in California, the Federal Aviation Administration announced today that it would seek to impose a rule requiring airlines to install anti-collision devices in their fleets. The agency also said it would set aside additional traffic control areas where private aircraft would have to carry equipment that automatically shows their altitude on radar. The single-engine Piper that collided with an Aeromexico jet Aug. 31, killing at least 81 people, did not have this equipment. Donald D. Engen, head of the aviation administration, said he was switching to a policy of forcing installation of anti-collision devices because the industry was not moving to do it voluntarily.

Federal health officials announced today that an experimental drug had markedly improved the health of a group of AIDS patients, adding months to the lives of some. They said thousands of victims of the deadly disease would soon be given access to the drug. The antiviral drug, azidothymidine, holds ''great promise for prolonging life for certain patients with AIDS,'' said Dr. Robert E. Windom, the Assistant Secretary for Health. The announcement today provided the first beam of hope in the battle against acquired immune deficiency syndrome. The drug, manufactured by the Burroughs Wellcome Company and also known as AZT, is the first to show effectiveness against the fatal disorder in controlled scientific studies.