Within the next few days, government scientists plan to detonate a hydrogen bomb 1,800 feet below the Nevada desert to test the secret X-ray laser, one of the most controversial components of President Reagan's "Star Wars" antimissile defense program.

Code-named Goldstone, the test is at the center of an increasingly rancorous dispute about the X-ray laser and its role as a potential weapon in the Strategic Defense Initiative. Although it was conceived at the Lawrence Livermore National Laboratory in California about five years ago and helped to spawn the Star Wars program, the X-ray laser only recently has become a contentious issue within the larger question of whether Reagan's antimissile defense vision should be pursued.

As envisioned by Livermore scientists, a hydrogen bomb detonated in space would release energy that a laser would convert into an instantaneous burst of X-rays. In theory, the aimed rays could destroy a Soviet intercontinental ballistic missile shortly after launch. After one shot, lasting about one-millionth of a second, the exploding bomb would destroy the laser.

Development of such a weapon is years away, and some scientists say they believe it will never be feasible. The Goldstone test will involve only an experimental device intended to demonstrate whether a sufficiently intense X-ray beam can be produced to merit development into a weapon.

The test had been set for yesterday morning, but was postponed because winds threatened to blow any escaped radiation toward Las Vegas, 104 miles to the southeast. Officials said the test would be carried out when the winds either die or shift toward less populous areas.

Neither SDI officials nor the scientists who designed the device at Livermore would say whether the explosion, expected to equal between 20,000 and 150,000 tons of TNT, is an X-ray laser test. Scientists familiar with the program, however, say that it is.

The current debate about the X-ray weapon erupted last month when it was learned that physicists at Livermore and its sister nuclear weapons laboratory at Los Alamos had discovered major flaws in previous laser tests in underground nuclear explosions.

Some of the flaws were in instruments intended to measure the X-ray beam's intensity and focus. Although the defects were known to render previous findings uncertain, some Livermore scientists say the laser's most ardent advocates described the results in misleadingly optimistic terms when they asked President Reagan and congressional leaders for an extra $100 million for the program.

"Scientific organizations such as Lawrence Livermore have an important responsibility to provide the most evenhanded information they are capable of providing," said Ray Kidder, a senior leader of hydrogen bomb research at the lab. "That's because the people making the policy back in Washington don't have the technical expertise to evaluate these things. They have to rely on us for good information to guide them. The lab has fallen a bit short of meeting that responsibility."

Among those identified by Kidder as overly zealous proponents are Livermore's hydrogen bomb pioneer, Edward Teller, a longtime Reagan friend, and his protege, Lowell Wood.

Shortly after a flawed test in March, Teller and Wood came to Washington with optimistic reports about the laser's progress and asked for the extra $100 million to speed the program.

"Every program needs a zealot and Lowell Wood is the zealot that this program has to put up with," Kidder said. "He believes with a religious fervor that the X-ray laser is going to save the United States from the Russians. He's absolutely convinced of it. He hates the Russians with a passion. You've got the Holy Grail zealot in Lowell Wood and right behind him is the political clout of Edward Teller. You don't want to base policy on the ravings of a zealot." Repeated efforts to reach Teller, Wood and other advocates of the X-ray laser at Livermore were unsuccessful. Some proponents of the research have argued that it is a legitimate part of the strategic defense effort, which is looking at a wide spectrum of potential technologies.

SDI officials also say they are not necessarily studying the X-ray laser for its potential as a U.S. weapon, but to see whether the theory can be translated into practice. If so, the officials add, it might be necessary for the United States to be able to defend itself against a Soviet version of the weapon.

Two weeks ago, when critics asserted that Livermore was planning yet another potentially flawed but still costly $30 million test, 30 members of Congress asked that Goldstone be delayed until they could be briefed on whether the defects had been corrected. Their request was rejected.

Among many controversies about the device, the most obvious is that the X-ray laser is a nuclear weapon being tested for a role in what Reagan has repeatedly called a "non-nuclear" defense system intended to make nuclear weapons "impotent and obsolete."

Other questions deal with the workings of the device and how it would be used in an antimissile system. Even the man nominally in charge of Livermore's nuclear program, George Miller, cautions against premature optimism.

"What we have not proven is whether you can make a militarily useful X-ray laser," Miller told Science magazine. "It's a research program where a lot of physics and engineering issues are still being examined."

Miller was recently named to the post when his predecessor, Roy Woodruff, quit and transferred to another Livermore division. Woodruff, who had formal responsibility for the X-ray laser program, would not disclose his reasons for resigning. But senior colleagues at the lab said he was "fed up" with "end runs" that Teller and Wood were making, bypassing Woodruff and going straight to Washington.

Other scientists at Livermore, senior physicists who are critical of the program but who asked not to be named, said previous tests had shown that the device does produce X-rays but that it was unknown whether they were strong enough to be useful.

One critic at Livermore said the Goldstone experiment may yield better information on this subject because of improvements made since the previous test. But he said the test would be more useful if delayed to incorporate other improvements.

Unlike many other elements of an antimissile system, the X-ray laser is not generally regarded as a space-based weapon. Instead it would be launched into space in the nose cone of a missile -- "popped up," in the jargon -- as soon as space-based sensors detected a Soviet attack. When the missile was high enough, its bundles of fibers would be aimed at a rising Soviet missile and the bomb would go off.

The necessity of a virtually instantaneous pop-up, critics say, would mean the United States would have to fire nuclear weapons into space without presidential authorization.

Teller has long argued that the pop-up approach is preferable to space-basing because any weapon in orbit is easily tracked and vulnerable to Soviet attack. If the Soviets planned a nuclear war, some strategists agree, their first step would be to use antisatellite weapons to knock out U.S. space-based defensive weapons.

But because any beam weapon can shoot only in a straight line, it must be high enough to "see" a Soviet missile over the Earth's curvature. This means the X-ray laser would have to be based close enough to the Soviet Union to minimize curvature. Thus, advocates envision the weapon as based in submarines near the Soviet coast. A new class of missile-carrying submarines would have to be developed to deploy the X-ray laser this way.

Furthermore, because X-rays cannot travel very far in air, the weapon can attack only during the brief interval after the target missile has left the atmosphere and before it has released its warheads.

If the Soviets knew the United States was relying on the X-ray laser, critics say, they could defeat the weapon by developing faster rockets that complete their "boost phase" within the atmosphere and release their warheads before the laser could fire, a strategy known as "fast burn." Because warheads are heavily armored to survive a fiery reentry into the atmosphere over their targets, they could prove resistant to an X-ray beam.

It has not been disclosed whether X-rays have been tested for their ability to destroy a rocket, but in theory they would cause a small explosion on the side of the missile that knocks it off course or dents the missile's metal skin, causing it to crumple. X-rays cannot penetrate a missile's skin but their energy could cause a surface layer of atoms to "boil off" electrons so suddenly that the recoil effect damages the missile.

The X-ray laser consists of two main parts, a hydrogen bomb and, surrounding the bomb, a collar of parallel bundles of straight, hair-thin metallic fibers. When the bomb goes off and in the split second before the blast destroys the whole apparatus, its radiant energy reaches the fibers, heating them until they glow, although not in visible light. Instead, the great temperature makes them give off X-rays.

X-rays, similar to visible light, are a form of electromagnetic radiation consisting of subatomic particles called photons. Each photon may be thought of as a tiny packet of energy. Unlike medical X-ray machines, which scatter photons in all directions and quickly dissipate their energy, the X-ray laser keeps the photons in nearly parallel paths and in waves that are all in step, or in phase. The energy stays concentrated in the beam, which in the vacuum of space can travel thousands of miles.

To produce the most intense beam from an X-ray laser requires the energy of a hydrogen bomb, in the form of the bomb's own X-rays and gamma rays.

Physicists know that laser photons from all sources do not follow perfectly parallel paths. They diverge at angles that can be calculated from the length and diameter of the fiber and the wavelength of the X-rays. The longer and thinner the fiber and the shorter the wavelength, the tighter the beam.

Scientists outside the Livermore program have calculated that laser fibers about six feet long and one-thousandth of an inch in diameter would produce beams that, at a distance of about 2,400 miles -- a typical range for the weapon -- would make a spot about 350 feet across.

Among the major questions to be answered in the Goldstone test are whether the beam is bright enough to be useful even after it has spread and whether there is some way to focus it more tightly to minimize the spread.

If not, the X-ray laser's future in Star Wars may not be bright.