THE UNITED STATES has four major vehicles for launching objects into space. One is nearly obsolete, and now in succession the three others have failed. Is that a fluke, or does it mean there is something fundamentally wrong in the space program? NASA, the agency most involved, prefers the theory of coincidence. Its spokesmen suggest it would be wrong to aggregate the three events and try to read a pattern into them. Maybe so.

The most recent failure, which occurred on Saturday, involved a Delta rocket carrying a weather satellite. The Delta had always been reliable; only 11 of 177 previous flights had gone awry, and more than 40 consecutive launches had been successful. But this time the first-stage engine prematurely shut off about 70 seconds into flight, the rocket started to tumble, and a safety officer blew it up. That followed by two weeks the failure of an Air Force Titan rocket that blew up five seconds after launch, the second Titan to explode in two attempts. Before Titan came the Challenger accident.

The Titan and Delta accidents would have drawn scant notice absent what happened to Challenger and what has been unearthed about NASA since. (The previous Titan accident last August was only a five-paragraph story on the major wire services.) But if the tendency four months ago in Congress, press and public was to lead cheers for NASA, the pendulum now has swung the other way. The post-Challenger investigations have shown that for years federal auditors complained of poor management at NASA; that in the case of the shuttle, serious questions were raised within the agency about safety and design, and were brushed aside; and that decision-making at certain critical points had about it all the orderliness and decorum of a clamorous crap-shoot.

Last week it was reported that as early as 1978 NASA engineers had expressed concern about the design of the leaking O-rings that are thought to have brought down Challenger; that a memo in 1979 labeled the joints these rings were meant to seal "completely unacceptable"; that in 1985 officials imposed a "launch constraint" on the problem, meaning no launches were to take place until it was fixed; and that a Marshall Space Flight Center official, Lawrence Mulloy, then signed six successive waivers to let the flights proceed anyway. The laws of probability seem to have taken it from there.

At Cape Canaveral yesterday, NASA staged a ceremony marking the 25th anniversary of the first manned American space flight, by Alan Shepard in 1961. NASA is justly famous for its PR. This was to remind us all of the glory days of the past and take the edge off the present unpleasantness. A year ago it might have worked; it always did before. Now PR isn't good enough. That is the least of what you would hope the agency has come to understand.