Secretary of Defense Harold Brown said yesterday that the Pentagon will embark on a major upgrading of the cruise missile in the aftermath of President Carter's cost-saving decision to stop production of the B-1 bomber.

Brown spoke at a press conference about improving the cruise missile as the Soviet government's new agency Tass, in the first Moscow reactions to the decision, criticized President Carter's choice of the air-launched cruise missile.

"United States has started a new round in the dangerous arms drives," Tass said in an unsigned dispatch from Washington. Washington Post Moscow correspondent Kevin Klose said the Tass dispatch could be against the cruise missile decision.

Despite any alarms Soviet leaders may sound, Brown indicated yesterday that the United States is now firmly committed to arming its bombers with the nuclear-tipped pilotless cruise missiles, which could fly about 1,500 miles into Russian on their own after launching.

"We have to continue to assure that our position on the cruise missiles in SALT (strategic arms limitation talks) does not interfere in any serious way with our plans for the incorporation of cruise misless into the strategic bomber force," Brown said, indicating the cruise missile cannot be nagotiated out of the U.S. inventory.

The Defense Secretary added that under the present schedule the air-launched cruise missile would be ready for installation on bombers in 1980. But he said this schedule will be accelerated, possibly advancing the deployment date. Contractors said they could hve cruise missile ready as early as 1978.

The immediate U.S. objective is to keep the aged B-52 bomber fleet in deployment by adding the cruise missile to its weaponry. But Brown said this is only the first step toward keeping the American bomber offense ahead of the Soviet defense.

"As we look ahead 10 or 15 years," he said, "the defenses are going to improve, but so also will the cruise missiles . . . I'm sure that the cruise missiles are going to get harder to intercept. We will be able, I know to program evasive action into them."

Other improvements, Brown said, include putting jamming equipment inside the cruise missile to foil the Soviet defense. And although Brown did not mention this yesterday, teh Air Force already is working on a supersonic-speed cruise missile to replace the present generation, which flies close to the ground at between 300 and 500 miles an hour.

Another possibility, still only in the talking stage at the Pentagon, is to divide the missile's single nuclear warhead into several smaller ones to overwhelm the defense.

Improvements already on the drawing board or being tested "will keep us in business with cruise missiles." Brown said in assessing this new direction in the arms race.

He stressed that the cruise missile will keep the bomber leg of the "triad" firmly in place through the 1980s. The triads is the Pentagon term for the offensive system of bombers, submarines and land-based missiles.

The triad strategy is to make it apparent to Soviet war planners that any nuclear attack on the United States could not wipe out enough of the nuclear arsenal to cripple its retaliatory power.

While Carter's decision appears to rule out negotiating away the cruise missile destined for the bomber force, Brown said cruise missiles for land bases, ships and submarines "are subject to current negotiations" with the Soviets.

It will cost about $700,000 to equip a B-52 bomber to carry and launch the cruise missile, Brown said. The Pentagon will study ways to modify civilian transports like the Boeing 747 as cruise missile launchers.

He said "at most" 250 B-52s would be assigned to the cruise missile role, leaving others for the tougher mission of flying low to penetrate Soviet defenses.

Reading a statement as he opened the press conference, Brown said that last year "it seemed to see me that the arguments for the B-1 had some plausibility." As he re-examined advances in cruise missiles, Brown said, he concluded that aircraft carrying them "will better assure the effectiveness of the boomber component of U.S. strategic forces in the 1980s" than producing the B-1.

Without specifying a figure, Brown said cancelling B-1 production in favor of putting the cruise missile on less expensive planes will save "many billions of dollars." The fiscal 1978 Pentagon budget, which Brown will seek to amend, contains $1.4 billion in production funds for the B-1. Much of this money will go into cruise missiles. Brown said, but there will be some left over.