Challenger's loss hobbles US space program. Significant delay in missions affects Europeans as well as US and sparks debate about high reliance on manned spacecraft

The loss of the shuttle Challenger and its crew has put the United States space program on hold. Investigation of the cause of Tuesday's tragic explosion will ground all shuttle flights for months, if not for more than a year. The four-shuttle fleet has been the US's main space transportation system, and this week's loss cuts that fleet's capacity by 25 percent.

Even when flights are resumed, this means that the launch of scientific, commercial, and military satellites and spacecraft, and many research missions, will be seriously delayed. In some cases, research missions may be scrubbed altogether.

Such loss of shuttle capacity will affect America's foreign space partners as well. For example, European and Soviet scientists, whose probes will intercept Halley's comet in March, have been counting on backup observations that were to have been made by ultraviolet (UV) instruments in the Astro UV observatory that Columbia was to carry into orbit March 6. There seems little likelihood of meeting that launch schedule.

Two other major space missions with critical timing also will likely be seriously postponed. These are the launches of the Galileo Jupiter exploring craft and the US-European Ulysses solar probe, which would use Jupiter's gravity to put it on course. This was to have been the first twin shuttle mission, with two craft on orbit at the same time. With a launch window of a few weeks opening May 15, Challenger -- now lost -- was to have orbited Ulysses, which would then be boosted on its way by an auxiliary Centaur rocket. The shuttle Atlantis was to follow, with the Galileo craft a few days later.

In an interview before Tuesday's tragedy, William J. O'Neil, manager of science and mission design for the Galileo Project at the Jet Propulsion Laboratory in Pasadena, Calif., explained that Earth and Jupiter have to be in a particular alignment for the spacecraft to reach the planet with the onboard course-correction fuel available. He said that if Galileo did not get off by early June, it would have to wait a year and a quarter for Earth to return to a favorable position in relation to Jupiter.

Now that wait seems inevitable. If Galileo did get under way this spring, it would have an opportunity to make a close inspection of the comet Amphritite. That opportunity for early inspection of an asteroid now seems lost. Mr. O'Neil said he doesn't think any other asteroid would be near Galileo's trajectory next year.

Postponement of Ulysses, which also needs the favorable planetary alignment, would seem especially ironic to the European Space Agency. This project began as a two-spacecraft exploration of regions of space over the sun's poles. One craft was to be supplied by the United States. But NASA reneged on that commitment in order to meet budget constraints, while fulfilling its committment to launch the European-supplied spacecraft on the shuttle. This further delay is likely to force ESA again to reassess the extent to which it can afford to commit its space future to cooperative projects with the US. It's bound to reinforce the positions of critics who question ESA participation in the US space-station program.

Already, West Germany has postponed a drive to recruit six more astronauts. A spokesman for the agency West German Experimental Aerospace Research was quoted by Reuters as saying, ``We must find the cause of the accident and safety must be established.''

Disruption of the shuttle's scientific missions also seems likely to reopen the general debate over the value of manned spaceflight vs. less costly unmanned launches of automated satellites and space probes.

The US Defense Department, which has been openly concerned about relying too heavily on the shuttle, has already won permission to continue buying Titan launch vehicles for critical spy and other military satellites. Loss of a fourth of the shuttle fleet will strengthen the DOD's position. Moreover, the first military launch from Vandenberg Air Force Base will be indefinitely delayed.

Manned spaceflight has had its critics since Alan Shepard's first hop off the launch pad in a suborbital test of the old Mercury capsule a quarter- century ago. Some scientists, particularly, have criticized manned missions as having relatively little scientific value.

Now these arguments are beginning to be heard again. Veteran space physicist James Van Allen of the University of Iowa has been warning against what he considers overemphasis on manned spaceflight. He is concerned that development of a manned space station could drain money from unmanned scientific space operations, just as the high cost of shuttle development did in the late 1970s and early '80s.

In another typical reaction, University of Minnesota astronomer Edward Ney has deplored the loss of life for what he considers a project of little scientific value. According to the Associated Press, he said, ``Putting men on the moon was probably the greatest bit of exploration in the history of mankind. I have all kinds of respect for that achievement, but not for putting up a transporter to haul junk and people who are sightseers.''

This will probably strike spaceflight supporters as ironic; critics denounced the moon landings, in their day, as a scientifically dubious stunt. As Rep. Jerry Lewis (R) of California, a member of the House budget subcommittee that oversees NASA funding, noted, ``America's future has always been with the horizons, and space to me has just been the next frontier.''

At this point, NASA officials expect to continue development of that frontier, as President Reagan has pledged, once they have found and corrected the cause of the Challenger explosion. But the next shuttle flight is likely to be preceded by a spirited national debate over manned spaceflight's value.