The Soviet Union has stunned the U.S. intelligence community by launching a new cruise missile-firing submarine which will make American aircraft carriers 10 times more vulnerable than they are now, Navy officials disclosed yesterday.

The jumbo submarine, code-named Oscar, is almost twice the size of the largest U.S. attack sub now at sea, and when in service will extend the lethal reach of Soviet anticarrier forces from today's 20 miles to 200 miles, they say.

Oscar is not bigger than the biggest U.S. submarine, the Trident. But the Trident is a ballistic missile sub, which has a different mission. The Soviets also have a larger version of that type, called the Typhoon.

Attack submarines are designed to sneak up on other submarines or surface ships and destroy them before being detected. Quietness, speed and diving depth often decide who wins this deadly battle of hide-and-seek. Critics of the main U.S. attack sub, the Los Angeles class argue that its size is a drawback; that smaller subs would be harder for the enemy to find. Oscar suggests Soviet naval leaders have not bought that argument.

Missile subs are basically underwater launching platforms for ICBMs.Here, too, the Soviet high command has gone the United States one better in size. The new U.S. Trident missile submarine, longer than the Washington Monument is high, has been more than matched by the Soviets' new Typhoon, which is about 50 percent bigger than Trident, according to analysts.

"Worst-casers" at the Pentagon warn that several Oscar submarines could surround a U.S. aircraft carrier, World War II wolfpack-style, and bombard it and escorting warships with accurate cruise missiles.

Navy and intelligence officials admitted in interviews they were stunned when U.S. spy satellites revealed last spring that it was a new cruise missile submarine the Soviets had been building in a giant shed at Severodvinsk shipyard on the White Sea near Archangel.

"We all misjudged it," one admiral said. "An intelligence gap," a top intelligence official said. One theory before Oscar slid out of the shed was that an aircraft carrier was being built there.

One Navy leader who has sifted through the top-secret information on Oscar cautioned against writing off carriers as sitting ducks. The Navy is well along on ways to find and kill such such submarines, he said.

"Concern, not panic," is how he portrayed the Navy attitude toward Oscar.

He said the Soviets' plan for sinking U.S. carriers has been to track them with eavesdropping trawlers, which would radio to nearby ships, submarines and planes a course for their cruise missiles. Then the missiles would guide themselves the rest of the way.

The effective radius for such a coordinated attack, this official said, is about 20 miles, partly because of the limited range of the cruise missiles on Soviet submarines. But the Oscar and its new cruise missiles will push that kill range out to about 200 miles, he added.

The Oscar is huge for a nuclear-powered attack submarine, about 10,000 tons compared to the 6,000 tons for the Los Angeles-class.

The Oscar is believed to be made of titanium, so it can go faster and deeper. Thus Oscar could turn out to be an underwater speedster like the Soviet Alpha titanium submarine, clocked at 40 knots, or faster than any U.S. sub. The United States may determine Oscar's capabilities during its sea trials by sending a submarine to clock it on test runs.

Another big unknown is how many Oscars the Soviets will build. They traditionally build a lot of different submarines but produce only a few types in quantity. The Soviets built only three Charlie II and two Papa cruise missile submarines, first spotted in 1973. Some analysts suggest the Soviet investment in building a giant sub like Oscar, about twice as big as Charlie II and Papa, indicates it is not just experimental, but rather the forerunner of a large new class.

The Navy is working on three lines of defense against Oscar: finding the submarine before its missiles are in striking distance of the carrier force; destroying the cruise missiles when they are launched; a close-in defense against missiles that get through the outer barrier of the task force.

It will take billions of dollars to do all this. Critics contend there is no way to protect the Navy's force of 12 to 13 giant carriers in the age of accurate, long-range cruise missiles, and that the money should go for a greater number of smaller, less-vulnerable ships.

Protecting the carrier in the future, Navy leaders said, will require buying more Tagos ships which tow a long string of microphones through the water to detect Soviet subs; cruisers armed with Aegis radar and missiles for tracking and firing missiles at incoming Soviet cruise missiles, and the Phalanx for close-in defense.

Phalanx would fill the air around the ship with bullets in hopes of stopping any cruise missiles which evade Aegis ship missiles.