As US space program officials probe the cause of last weekend's failure of a Delta rocket -- the third such debacle in 14 weeks -- some of the impact of the recent string of accidents are becoming clearer: The United States faces at least a temporary grounding of almost its entire spaceflight fleet. This means the nation has virtually no way of launching commercial, scientific, and defense satellites at a time of growing world dependency on space for national-security surveillance and other military and civilian functions.
The US hiatus could boost the rapidly developing space programs of other nations, especially France, China, and Japan, which are increasingly competing with the US in the satellite-launching business. But experts say there will be no wholesale shift of commercial customers to foreign vendors.
The succession of accidents does, however, erode morale at the National Aeronautics and Space Administration (NASA) and intensify questions about the agency's maintenance and management procedures.
Former NASA administrator James M. Beggs says the Delta failure ``is another blow to the morale of the organization.'' But he adds, ``There is nothing wrong with their competence. They have just had some very bad luck.''
NASA officials speculate that Saturday's failure may have been the result of a short circuit in the rocket's main engine.
The immediate problem facing the nation's space program is the lack of launch capability. With the failure of the unmanned Delta rocket last Saturday shortly after liftoff from Cape Canaveral, Fla., the US temporarily lost a crucial third leg of its launch system.
The shuttle program has been grounded since the destruction of the Challenger in January. The unmanned Titan rocket program -- chief vehicle for launching military spy satellites into orbit -- is down because of the recent explosion of an Air Force Titan 34D.
Lawrence J. Ross, head of the eight-member NASA panel investigating Saturday's incident, said Monday that three planned launches using Deltas will be grounded until the cause of the problem is found and remedied. The next Delta launch, of a military communications satellite, had been scheduled for Aug. 14. An Oct. 9 launch of a weather satellite and another scheduled for 1987 have also been put on hold.
Saturday's Delta launch vehicle, carrying a $57.5 million weather satellite, was destroyed by radio command 91 seconds after blastoff when an engine malfunctioned and threw the spacecraft out of control.
All launches of the usually reliable Delta rocket -- a workhorse in the nation's ``expendable launch vehicle'' fleet -- have been suspended until an investigation into the accident is completed. This is expected to take at least two months. That leaves only one other major launch system -- the Atlas-Centaur, also a non-reusable rocket -- in the US program. But it, too, may be affected by the recent misadventures.
An Atlas-Centaur is scheduled to boost a military communications satellite into orbit May 22. But NASA officials suggested Monday that this launch might be delayed because the Atlas and Delta use somewhat similar engines.
Officials want to know what went wrong with last Saturday's launch before pressing ahead with either vehicle.
NASA has only three Deltas left in its inventory, along with just three Atlas-Centaurs. A smaller rocket, the Scout, is used for scientific purposes.
The temporary loss of three key launch systems has put a severe crimp in the nation's ability to hoist a wide variety of payloads into space, from communications satellites to military equipment to vital weather sensors. It also complicates NASA's ability to catch up on a growing backlog of space-launch bookings.
Space agency officials have been considering moving some payloads from the shuttle schedule to expendable rockets, partly to forestall paying customers jumping to overseas competitors. That option has been temporarily narrowed with the Delta and Titan failures.
Nevertheless, a stampede of commercial launch business to other countries is unlikely. One of NASA's chief rivals -- Arianespace, the French space group -- is booked with launch flights through early 1989. It may also be two years or so before China can put up big satellites.
``It will take the Europeans a couple of years to get more launch capacity,'' says David Lippy, president of the Center for Space Policy Inc., a Cambridge, Mass., consulting firm. ``By then the shuttle will be back on line.''
Ariane, which has had some launch failures of its own, did add one extra flight each to its 1987 and 1988 schedules. But ``as far as our business is concerned,'' the recent accidents in the US ``haven't made any difference,'' says Jacquline Schenkel of Arianespace Inc. in Washington, D.C.