The Bush administration yesterday unveiled a $290.8 billion defense budget for fiscal 1992 that takes the first step in the direction of a smaller, post-Cold War military, but hedges the nation's bets on the future of East-West relations.

The budget would continue spending on a number of major strategic weapons systems designed to confront Soviet power -- including $4.8 billion for four more B-2 "stealth" bombers, $5.1 billion for the Strategic Defense Initiative and $2.3 billion for the SSN-21 nuclear-powered attack submarine.

Defense Secretary Richard B. Cheney said yesterday that the threat of a short-notice, global confrontation with Moscow appears to have receded. But he added that recent developments in the Soviet Union have been "of concern, not only to those Soviets who were in hopes of reduced militarization of Soviet society and greater democracy, but to all of us who have anticipated in the West that we would see continued improvement, domestically, inside the Soviet Union."

If assumptions about a receding threat change, he said, the administration will ask Congress to halt the planned five-year reduction of forces at a higher level than now envisioned. "There's enormous uncertainty about what's going to transpire inside the Soviet Union in the future," he said. Cheney said Soviet missile and submarine development has moved ahead despite troop cuts in Eastern Europe.

The defense budget for fiscal 1992, which begins Oct. 1, omits the costs of the Persian Gulf deployment and war. Those will be handled in a special request to Congress later this month. But Cheney yesterday used the success of the Patriot missile and the F-117A stealth fighter-bomber in the war to buttress his case for the B-2 and SDI.

He called it "vital" to continue with the B-2 in light of the proven advantage of stealth technology, and said Iraqi Scud missile attacks were grounds for future deployment of an anti-missile defense.

The Pentagon's long-range plan for a leaner, faster, more adaptable military calls for sweeping across-the board force reductions by 1995. Active and reserve Army divisions would be cut from 28 to 18, aircraft carriers from 14 to 13, tactical fighter wings from 36 to 26, ships from 545 to 451 and strategic bombers from 268 to 181.

Cheney called it "the absolute minimum, irreducible capability that we have to have to defend the United States."

But within the framework of long-range cuts, Pentagon officials found money for major strategic systems such as the B-2, and for high-priority conventional weapons for each of the major services. These include a new aircraft carrier for the Navy, and continued development of new-generation high technology systems for the Army and Air Force, including the LH helicopter and the Advanced Tactical Fighter.

If the purchase of these big-ticket items begins in mid-decade as planned there will be a bulge in the Pentagon procurement budget in 1995, even as the overall level of defense spending declines.

The new generation of high-tech weaponry apparently will be financed by terminating many existing weapons, including some that have proved effective in the Persian Gulf War, according to Gordon Adams of the Defense Budget Project.

Among weapons that have already been terminated are the Navy's F-14D fighter, the Air Force's Maverick missile, the Army's M-1 tank and Apache helicopter, and the Air Force's F-15E fighter.

Yesterday the Pentagon announced a lengthy list of additional phase-outs, including the Marine Corps' LHD amphibious assault ship, the Army's Bradley Fighting Vehicle, the Air Force's F-16 fighter, and the upgrade of the F-14. The budget envisions decommissioning the last two U.S. battleships, the Missouri and Wisconsin, by the end of September.

Noting that both vessels have been firing Tomahawk cruise missiles in the Persian Gulf War, Cheney said yesterday, "I'd like to keep the battleships, but I can't afford it."

Congress is expected to raise sharp questions about a $2.3 billion increase for SDI above the current year. The administration budget nearly doubles the funding for research into a space-based rocket and sensor system intended to protect against a large-scale ballistic missile attack.

Ironically, the 1992 budget requests no new funds to buy additional Patriot missiles. In its projections last year, before the outbreak of the gulf war, the Army had planned to ask for an additional 440 of them in 1992.

The Army could yet ask for more Patriots as part of its separate request relating to Operation Desert Storm. But congressional sources said last week that they intend to police the supplemental budget request associated with the war to keep the Pentagon from hiding regular expenses in its war appropriation.