Twenty-five years after Sputnik, outer space has lost some of its original glow.

Americans whose youthful brains danced with visions of space colonies and interplanetary travel have become mature adults, infused with new skepticism about technology, government planning and massive spending, and preoccupied--at least in the long gaps between live-TV broadcasts of space-shuttle missions--with matters closer to home.

Daniel Deudney is a member of that generation who thinks the two concerns, home and space, are not so unconnected. The 28-year-old Deudney, an energy and resource specialist at the Worldwatch Institute, has written a sternly worded report, released yesterday, that condemns the "militarization of space" by both the United States and the Soviet Union, belittles such "grandiose hallucinations" as asteroid mining and satellite collection of solar power, and urges a new international effort to use space "to assist problem-solving on Earth."

In the 1950s and '60s, says Deudney, fear of Soviet aggression and superiority helped get the U.S. space program under way. But in the last decade, military concerns have become an obstacle rather than a spur to discovery, he says.

"The reason that it happened is that at first the military was taking us to near space, and if the military had then gone on to deep space, they would be at the cutting edge. But they're not interested in going into deep space. They're just interested in developing the near-space military potentials, and this is crowding out near-space non-military uses."

Both the United States and the Soviet Union devote about 70 percent of their space budgets to military purposes, Deudney estimates, so the competition for dollars and rubles is a large part of the problem. "The budget of the U.S. planetary science program," he says, "has been cut so deeply in the last year that expensive probes already far from the Earth will be turned off." (This is a prediction others dispute.)

He warns against the hazards of secrecy--the secrecy that bars state-of-the-art radar and Earth-monitoring equipment from nonmilitary satellites, and the larger secrecy that compels the two superpowers to work along parallel rather than complementary paths. And he sees satellite killers and other space weapons as a leap forward in the arms race that will "make each country more vulnerable to a first strike and will not give either country a defensive advantage, despite enormous costs." The Soviets may have the temporary edge in anti-satellite weapons, he says, but the U.S. response--a homing missile that can be launched from a high-flying fighter plane without warning--"is a technological advance into a whole new plateau of danger."

Both countries should redirect the military portions of their space efforts toward weapons surveillance, Deudney argues, to make arms control agreements easier to verify. A United Nations conference on outer space ("Unispace"), which convenes next Monday in Vienna, will be a sham, Deudney insists, unless it decides to tackle the military issues that have been kept off the agenda at the behest of the Americans and Russians.

Another target of his report is the Reagan administration's proposal to have private enterprise take over the LANDSAT network of satellites intended to monitor the Earth for such civilian purposes as farming, forestry, mining, transportation, map-making and long-term weather prediction. The possibilities of such a system are tremendous, says Deudney, noting that U.S. strides have enabled us to predict recent Soviet wheat harvests more accurately than the Soviets themselves.

But making LANDSAT a profitable and a purely domestic effort won't work, he says, because "the largest purchaser of LANDSAT images right now is the government itself, and unless the government would say to the private sector, 'We're going to guarantee purchases years into the future,' no private investor is going to put up that kind of money up front."

Besides, different purchasers will be interested in different kinds of information, and "the process of making the technology fit into the users' concerns is inherently a process of internationalizing the technology," says Deudney.

There are also fears that a LANDSAT system in private hands, selling its findings to the highest bidder, will exploit Third World countries. "If the oil companies have more information about their resources than they do," he explains, "they the countries think they'll be at a disadvantage in negotiations." Indonesia already is leading a campaign to give every country effective control over any such monitoring of its territory, and this kind of pressure could increase.

Another concern of the Third World is that the U.S. "will saturate their media markets with direct-broadcast satellites." The U.S. has dismissed proposals to restrict direct broadcasting, but Deudney thinks these nations "have a legitimate complaint, and what we need to do is transfer the technology to them so they can do the same thing . . . We need to buy them into the system. If they are engaged internally in large-scale information acquisition and transmission, then their feeling of being exploited by the system will diminish."

Because of military preoccupations, the United States risks losing out to Western Europe or Japan in some of the commercial uses of space, according to Deudney. France's Earth-monitoring system, for example, will offer images with twice LANDSAT's resolution, "not because of French technological innovation," he says, "but because the U.S. military makes NASA use low-resolution sensors for fear of revealing secret technology."

He has saved some of his most acid rhetoric for the promoters of schemes to collect resources and energy from space on a large scale. SUNSAT, a solar-power satellite plan proposed by physicist Peter Glazer in 1968, would require unpredictable technological breakthroughs, cost $1.5 trillion to $3 trillion, and, says Deudney, involve so many environmental hazards as to constitute "a shot-in-the-dark experiment with the human race's one habitable environment--the Earth's atmosphere."

Not true, says former astronaut Phil Chapman, now with the Arthur D. Little Co. in Boston. "All those objections have been thoroughly answered. The environmental arguments are mostly nonsense and red herrings. The real opposition to the solar-powered satellite is from the 'small is beautiful' people." The only remaining issue is how much such a system will cost, he says, "and the only way we're going to get the answer is to spend enough money to find out."

Deudney also weighs in against proposals for large manned space colonies. "Life in space for the foreseeable future will be like that in a submarine, an offshore oil platform or an Antarctic mining camp--dangerous, cramped, isolated and uneventful," he says.

Here, too, the feeling is not unanimous. Physicist Gerard O'Neill, of the Space Studies Institute in Princeton, N.J., predicts that within a century a billion people will be living in space colonies built from lunar material. "We regard the question of space-colony design as essentially a solved problem," O'Neill says. "The population density will be no higher than, let's say, San Francisco County, and there will be easy and inexpensive travel between one space colony and another."

Deudney calls such visions "misleading to the point of fraud," but cautions that he is talking only about the short range.

"Our longer-term destiny may be to explore deep space," he says, "and doing so may be the most exciting adventure of the species, but we have to start thinking about securing the base from which this venture will be launched, which is, inevitably, the Earth.

"We have to have an attitude toward space more like the one Moses had toward the Promised Land. We need to prepare ourselves for entering it rather than drop everything and rush into it."