Star Wars research is focusing on a concept called "Brilliant Pebbles," consisting of thousands of satellites under 3 feet long and designed to knock down enemy missiles, says Defense Secretary Dick Cheney.

Cheney told Congress on Tuesday that he remains a strong advocate of Star Wars, known formally as the Strategic Defense Initiative, but is recommending that the budget for fiscal 1990 be cut to $4.6 billion from the $5.9 billion proposed by former President Reagan.He said President Bush "believes very deeply that we need to go forward with strategic defense."

Much SDI research will focus on the Brilliant Pebbles concept, said Cheney, although SDI officials later said that weapon is one of several space-based anti-missile satellites under consideration.

The budget level for Star Wars "will buy us the capability to look aggressively at Brilliant Pebbles, said Cheney. "If Brilliant Pebbles does not work out, the ultimate deployment date of the current space-based missile program would slip by two years." He did not set a date.

Brilliant Pebbles drew backing from the outgoing SDI chief, Lt. Gen. James Abrahamson, who predicted in a Feb. 9 memorandum that it could be deployed in space for about $25 billion, far under estimates of $45 billion for other SDI orbital systems.

The concept calls for between 3,000 and 5,000 satellites, about three feet long and weighing less than 100 pounds apiece, to be placed in orbit up to 400 miles above the Earth, according to retired Lt. Gen. Daniel O. Graham, a strong backer of Star Wars.

Each satellite would be housed in a protective cocoon, called a "life jacket," from which it would be ejected in time of war. If everything worked, sensors aboard the satellites would spot and track enemy boosters, and rockets would propel the "pebbles" toward the boosters, destroying them before they could release their warheads.