Though the helicopters of the U.S. rescue mission in Iran were equipped with special explosives designed to destroy the secret material aboard, departing commandos failed to detonate them, thus handing the Iranians an intelligence coup, U.S. officials disclosed yesterday.

The officials confirmed that the U.S. commandos had taken along wire and thermite explosives for the specific purpose of destroying sensitive papers and gear.

But, as fires from burning aircraft lit up the desert night at the refueling rendezvous point last Thursday and touched off ammunition, the 180 commandos and air crewmen were ordered to rush aboard their C130 transports without waiting to blow up the helicopters.

With all that ammunition flying around in the dark, the commander on the ground, Col. Charles Beckwith, apparently feared that his five remaining C130 transports at Desert One might be set afire, stranding his team on the desert 500 miles inside Iran.

A Pentagon official said the commando team had been dragging the helicopter that could not take off from Desert One away from the refueling site, apparaently with the idea of blowing it up, when another helicopter collided with a C130 full of fuel. The collision set both aircraft on fire and touched off the ammunition.

Another bit of bad luck was revealed yesterday when a Pentagon executive told Congress the helicopter that got caught in a sandstorm and returned to the carrier Nimitz in the Arabian Sea was the one carrying gear for repairing hydraulic systems.

Two of the RH53 choppers experienced hydraulic failures, one on the way to Desert One and the second after it landed there. Whether they could have been repaired that first night and kept the mission from being aborted is another of the unknowns piling up about the operation.

Exactly how big an intelligence grab the Iranians scored in going through the six helicopters abandoned at Desert One has not been disclosed. But the Iranians already have displayed enough sensitive photography and maps from the choppers to disturb U.S. intelligence specialists. They fear some highly secret code gear may have been lost to the Iranians as well.

Among the "friendlies" who took risks to help the attempted rescue of the 53 hostages in Tehran were some Iranians. One fear, confirmed, is that the documents left in the helicopters might enable the Tehran government to find these Iranians.

One government intelligence specialist termed it "slopy planning" to let anybody in the American rescue party carry his wallet, as was done on this mission. The Iranians have displayed a serviceman's wallet left at Desert One.

Asked whether the rescue team was forbidden to carry such detailed identification, a Pentagon spokesman said no such restriction had been imposed.

The spokesman also said the rescue team did not blow up the first of the seven helicopters abandoned on the desert for fear the resulting fire would alert the Iranians to the mission. The pilot of this helicopter landed short of Desert One after experiencing problems with his controls.

"All the classified equipment and material were destroyed," said the Pentagon in reference to the secret gear on that first helicopter.

The 50 members of the Delta Detachment commando team whose mission aborted in the desert returned to home base at Fort Bragg, N.C., on Tuesday.

Although few troopers would talk to reporters who greeted them at the Fayetteville Municipal Airport, the Associated Press said one complained:

"You've got a mission. You know you can do it, and somebody tells you to pull out."

The commandos were wearing civilian c lothes and carrying black shaving kits but no luggage.

In a related development, The New York Post reported yesterday that some of the helicopters were doused with a combination of salt water and fire-extinguishing foam when a crewman accidentially set off the sprinkling system 10 hours before taking off on the first leg of the rescue effort from the carrier Nimitz.

The Pentagon confirmed that five choppers had been doused for 60 seconds, but said this "did not in any way contribute to any of the problems" experienced by the choppers after takeoff.