WHAT IS THE Intelligence Support Activity, and what has it been up to?

Until now, the existence of this component of the U.S. Army has never been disclosed. But according to a number of well- informed sources, the Intelligence Support Activity has been responsible for a number of illegal covert actions conducted without either a presidential finding or a report to the intelligence committees.

Early in 1982, the congressional intelligence committees learned of the ISA's actions -- which they declined to enumerate -- and conducted an investigation. Subsequently, the matter was referred to the Intelligence Oversight Board, an executive committee charged with examining questions of legality.

Although the organization came to the attention of Congress because of its involvement with Bo Gritz in 1981, apparently after the CIA's own unsuccessful operation in Laos, the Gritz mission was said to be "just a small part" of the ISA's activities. Several sources said the CIA had objected to the actions, which were approved and conducted outside normal channels. The sources said the ISA had conducted operations worldwide and that it is still active in Central America. Its current activities were said not to violate the law.

Rep. Charles Rose (D-N.C.), who was chairman of the House oversight subcommittee last year, declined to comment on the ISA's activities. But he said he was concerned that after the 1980 election "word went out that now Reagan is president and covert action is okay. There are lots of guys sitting around in the intelligence bureaucracy saying, 'Wouldn't it be nice if we could get one of those, too?' So the committee has had a hard time keeping an eye on an ever-expanding frontier."

Congressional sources said the Defense Department had made an effort to create yet another clandestine intelligence organization last year. They said Pentagon officials had argued that the CIA was not sufficiently responsive to their needs and that traditional military intelligence units were too visible. They requested funds in the 1983 budget to set up a new, secret intelligence organization with worldwide authority to conduct "human intelligence" espionage operations. The sources said the request had not been granted, in part because the experience with the ISA had created doubts that the new agency could be controlled.