July 23, 1983

The man who is believed to be the leader of Omega 7, the anti-Castro terrorist group, was arrested in Miami yesterday afternoon. According to Federal authorities, Omega 7 has been one of the most active terrorist groups in the United States. It has taken responsibility for at least two murders and more than 30 bombings in Miami, New York, New Jersey and Washington in the last seven years. The suspect, Eduardo Arocena, was charged with plotting to assassinate the Cuban Ambassador to the United Nations in New York more than three years ago.

The International Airport here came under rocket fire today and heavy artillery duels followed between Lebanese Christian and Moslem Druse militia forces in the nearby mountains. At least 21 people were reported killed and 45 wounded. Three Americans - two marines and a Navy enlisted man - were among the wounded at the airport. Most of the casualties were in Christian districts. The toll in Druse areas was not immediately known. Nor was it definitely established at once who fired at the airport, although the Lebanese Army said the rockets - 15 Sovietbuilt surface-to-surface missiles - had come from positions in Shuweifat, a Druse town four miles to the southeast.

Rita M. Lavelle, a former Federal environmental official, today was found not guilty of contempt of Congress after two days of testimony about her failure to appear at a Congressional subcommittee hearing. Miss Lavelle, smiling, said afterward that the verdict ''strengthens my faith in the system, the American system, that it will work.'' Her dismissal as head of the Environmental Protection Agency's toxic waste disposal program Feb. 7 touched off a storm of charges of wrongdoing aimed at Miss Lavelle and others at the agency. Verdict Cannot Be Appealed The jury verdict in Federal District Court today ends the Government's contempt-of-Congress case against Miss Lavelle. The prosecution cannot appeal a jury's verdict in a criminal case because of the Constitution's protection against double jeopardy. However, the Justice Department is apparently still looking into allegations that she may have committed perjury in Congressional testimony on other occasions.

A police helicopter and a commuter seaplane collided over Brooklyn yesterday morning, sending the helicopter into a vacant building below and the plane into the choppy water of New York Harbor. The two police officers in the helicopter were killed, and two men were trapped in the seaplane when it sank. Moments before the seaplane went under, two passengers escaped into the water. One swam to shore and the other was pulled out by tugboat crewmen who dived into the water to make the rescue, trying in vain to keep the plane afloat by tying ropes to it. Tail Rotor Torn Off The helicopter's tail rotor was torn off by the the collision. The blue craft flipped through the air, hit a three-story brick building, scraped down the building's side and crashed through the roof of a vacant garage. One witness said that one of the policemen tried to jump out and grab the roof of the building but could not hold on.

President Reagan has approved a plan calling for a substantial increase in American military involvement in Central America and preparations for a possible limited military blockade of Nicaragua, senior Administration officials said today. Military operations that the United States will soon conduct in Central America and the Caribbean are designed to lay the groundwork for the expanded American presence and the possible quarantine, the officials said. The series of air, sea and land operations, which are scheduled to begin next month, are to last a minimum of six months. In public comments officials have described the exercises as routine.