The United States intends to fire a cruise missile from under water next week and for the first time let it fly down range under its own power.

If all goes well, the Navy Tomahawk will burst out of the Pacific near California's San Clemente Island, sprout tiny wings from its missile body and fly on its compact jet engine some 80 miles down range. Its full range exceeds 2,000 miles. It can carry a nuclear warhead.

The scheduled test is one more bit of evidence that new weapons with enormous killing power are being born while politicans talk about calling off the arms race.

The point of no return is fast approaching for other American super-weapons besides the cruise missile, including the B-1 bomber, the Mark 12A nuclear warhead with enough accuracy to destroy Soviet missiles, and the blockbuster intercontinental balistic missile called the MX.

Of all these weapons, the cruise missile has proved the biggest inpediment to U.S.-Soviet agreement at strategic arms limitation talks (SALT).

In the absence of an agreement, President Carter apparently has opted for the strategy of continuing to develop the cruise missile and other weapons in hopes of putting pressure on the Soviets to negotiate a slowdown of the arms race.

A Soviet arms specialist warned in an interview that this "bargaining chip" strategy will lead to "an action-reaction" as American and Soviet military leaders push for more and more new weapons.

Backers counter that the cruise missile not only strengthens Carter's negotiating hand but will save money, offset the Soviet edge in blockbuster intercontinental missiles, and reduce Soviet fears of a first strike because it is too slow to use in surprise attack.

The American cruise missile is a long way from the V-1 buzz bombs Hitler fired at Britain during World War II. But now, as then, the cruise missile is basically a small airplane without a pilot. It can carry either a nuclear or conventional warhead in its nose.

The Navy wants the cruise missile primarily for knocking out enemy ships.

The Air Force sees it enabling bombers to stand safety back from enemy defenses, letting the missile take the bomb the rest of the way to the target. The Air Force also envisions it as a replacement for the "quick reaction alert" fighter-bombers based near the NATO front.

William P. Clements Jr., former deputy secretary of defense, "fell in love with cruise missile," according to one Pentagon executive, and gave it a big shove just before he left office.

Clements called it "the most important prgram we have under way in regard to its potential" and one that "is at least 10 years ahead of the Russians." Next week's test indicates Carter is solidly behind the cruise missile.

The two big reasons the new American cruise missile so effective are its engine and its guidance system.

The Williams jet engine, weighing only about 130 pounds, can propel the missile over 2,000 miles on a small load of fuel. Only a foot in diameter and a yard long, the engine fits neatly into thepencil-like Tomahawk, which is 21 feet long and 21 inches in diameter. The Minuteman IIIICBM, for comparison, is almost 60 feet long and is six feet wide at its thickest point.

The Tomahawks' smaller size is one reason its cost, counting research, is $1.5 million a missile. This compares to $9 million for Minuteman III and $100 million for the Air Force B-1 bomber.

If next week's next test launch were a wartime shot against a land target, the Tomahawk cruise missile would be shot out of a torpedo tube and then leap skyward on the strength of its small rocket motor.

Once clear of the waves, the jet engine would start automatically and propel the weapon low over the water toward land. Once over land, the missile's Terrain Contour Matching guidance system would take over.

"Feeling" the ground below with radar fingers, the guidance system would match the actual contour with that on the map in its mechanical brain. If radar bouncing off a hill showed the missile off course, the brain would adjust the fins to put Tomahawk back on its plotted path.

The same mechanical brain would guide the cruise missile shot from one place on land to another, achieving pinpoint accuracy. Navy technicians predict Tomahawk will hit within 10 feet of its target because it can correct its course as it flies.

The Navy plans to buy 1,264 Tomahawks for $2.2 billion and the AirForce 2,357 for $2.9 billion.

Asked last weekif the cruise missile was a vital weapon, Defense Secretary Harold Brown stopped short of that characterization but called it "very important from a military point of view," both for conventional and nuclear warface. The Tomahawk could pack the explosive power of a 500-pound conventional bomb, or burst with a force of about 200 kilotons if its warhead were nuclear.

There are critics of the missile development program, such as Sen. William Proxmire (D-Wis.).

He claims that between $165 million and $373 million could be saved if both the Navy and Air Force bought the weapon from the same contractor - General Dynamics. Under present plans, the Air Force wants to buy the missile from Boeing.

Proxmire also recites a General Accounting Office study that describes the program as characterized by "confusion and uncertainty."

But his criticisms have not slowed the advance of the cruise missile into American arsenal.