The U.S. forces involved in the Iran mission are part of a "counterterrorist" unit stationed at Fort Bragg, N.C., and jocularly called "Charlie's Angels" because its commander is Col. Charles A. Beckwith.

Precisely when the unit was formed is unclear, but Fayetteville, N.C., papers reported its presence in 1978 and have since kept tabs on it.

It is referred to in various places as the "Blue Light" unit and as Project Delta in imitation to the Vietnam special forces unit of that name.

Beckwith commanded Project Delta when he was in Vietnam.

The unit reportedly consists of 200 to 300 men drawn from all branches of the service. They are specialists in demolition, communications, and undersea (frogmen) operations.

"They can handle anything from .22-calibre pistols with silencers up to an antitank weapon," said one are similar to those at the staging site in Iran.

The initial purpose of the unit was to provide Entebbe-like strike force, with extreme versatility, to counter terrorist operations against Americans abroad. The typical mission envisioned was recapturing Americans taken prisoner by international airline hijackers.

In 1978, Ambassador Heyward Isham, the U.S. special ambassador to combat terrorism, was quoted as saying these forces wouldn't be used except outside the U.S. and with the permission of the host country.

Isham is no longer the special ambassador. The job is now held by Anthony Quainton, the State Department said.

The unit reportedly operates outside the normal chain of command of the armed forces. Through Col. Beckwith and an officer identified as Maj. Gen. Jack Mackmull, it is directly linked to the special ambassador and the Joint Chiefs of Staff and the White House. It is under orders of the president directly through this linkage, according to reports.

According to people on the scene in Fayetteville, members of the Blue Light/Charlie's Angels unit maintain low visibility at Fort Bragg. They are quartered on the post with other units to preserve anonymity, rather than being quartered as a single unit.

Their headquarters; however, is said to be the former Fort Bragg stockade.

One soldier interviewed yesterday at the sprawling base said a chain link fence surrounding the former stockade had been filled in with green strips of plastic sheeting "to hide what goes on inside."

Sources say a good many of the 200 to 300 men in the Blue Light Unit had previously served with special forces in Vietnam.

The strike force apparently had quietly been removed from Bragg several months ago, reassembled at a desert site in the southwestern U.S. for training, and subsequently moved to a takeoff point somewhere in the Middle East.

Navy officials in Norfolk, Va., refused to discuss any aspect of the operation, but military sources confirmed that the RH-53 helicopters, the Navy's largest, and their crews came from at least one of three squadrons based at the U.S. Naval Air Station there. Each squadron has six helicopters and about 230 people.

An undisclosed number of helicopters and crew were transferred from Norfolk to the Pacific Fleet last November. There were unconfirmed reports that the squadrons trained for the rescue mission somewhere in the Arizona desert, where conditions are similar to those at the staging site in Iran.

The 25,000 pound helicopters, built by Sikorsky of Connecticut, are nearly 90 feet long and 24 feet high and are powered by two jet turbine engines, according to Navy officials in Norfolk. They can travel as a maximum speed of 180 miles per hour and can go up to 700 miles without refueling. One of the helicopters set a distance record last year by flying nonstop from Norfolk to California, refueling en route in the air.

The helicopters, nicknamed "sea stallions," are primarily used as minesweepers at sea and the three squadrons are known as Helicopter Mine Countermeasures Squadrons 12, 14 and 16. When used for minesweeping, Navy officials say the helicopters require a pilot and co-pilot as well as two-to-three additional crewmen to operate the anti-mine equipment.

The helicopters can also be used to carry cargo and personnel. With minesweeping equipment removed, the helicopters can carry up to 40 passengers along with a pilot and co-pilot, according to Cdr. Jim Lois, spokesman from the Atlantic Fleet Naval Air Force in Norfolk.

Navy officials said the three squadrons comprise the Navy's entire fleet of 18 RH-53s, which cost approximately $3 million each. The loss of five helicopters in Iran amounts to nearly a third of the fleet. There were unofficial reports that about a half-dozen other RH-53s were sold to the Iranian armed forces before the fall of the shah.