WASHINGTON (AP) _ President Bush threatened a veto Monday as the House debated a $291 billion military budget that slashes his proposed spending on the Strategic Defense Initiative and the B-2 stealth bomber.

Despite Bush's warning, the House accepted the recommendation of its Armed Services Committee to trim the president's proposed SDI allocation from $4.6 billion to $2.7 billion in fiscal 1992.

The acceptance came through the chamber's rejection of a more severe measure that would have reduced SDI to a research program with a budget of $1.1 billion. The amendment failed, 266-118, leaving the committee recommendation unchanged as the House moved on to other sections of the bill.

In a letter to House Minority Leader Robert Michel, R-Ill., Bush accused members of the committee of targeting vital strategic programs and using the funds for weapons built in their own backyards.

''While cutting funding for these and other crucial programs, the bill funds unneeded items such as excessive procurement of aircraft and other weapons systems,'' Bush said.

The committee's bill also terminates work on the B-2 bomber at the 15 planes in production.

The package for the fiscal year beginning Oct. 1 increases spending on conventional weapons that proved successful during the Persian Gulf War, including the F-15 and F-16 jet fighters, the M-1 tank and the Patriot missile.

The president said fiscal constraints on creating armed forces to meet future challenges means ''there is no room for pork-barrel spending or politics as usual in Congress.''

The defense package reflects the panel's view of the diminishing Soviet threat by withholding funds for big-ticket strategic weapons and directing the Pentagon to test fully before buying, proponents say.

''More than any other bill in recent years, this bill is a product of lessons learned in the real world,'' Rep. Les Aspin, D-Wis., chairman of the Armed Services Committee, said on the House floor.

The ranking Republican on the panel, Rep. William Dickinson of Alabama, said he could live with the bill ''but some parts cause me some pain.''

''The bill leaves the nation without a coherent strategic modernization program,'' Dickinson said, referring to the cuts in SDI and the B-2 bomber.

Among the major provisions in the package are a reduction in Bush's request of $5.2 billion for SDI and theater missile defenses to about $3.5 billion.

The Armed Services Committee approved $2.7 billion for SDI, but provided no money for the concept of Brilliant Pebbles, in which space-based interceptors would search out and destroy enemy missiles.

The committee, however, earmarked $858 million for theater missile defenses, such as the Patriot, and designated the Army, not the SDI organization, as the lead agency to oversee the program.

Proponents of the panel's bill cite the growing threat of short-range ballistic missiles from developing countries such as Iraq as the rationale for increasing funds for theater missile defense.

The collapse of the Warsaw Pact warrants a cut in spending on exotic, long- term technologies like Brilliant Pebbles, say the bill's sponsors.

The committee's bill would halt work on the B-2 bomber at the 15 in production. The committee rejected the Air Force's request for $3.2 billion to buy four more planes in fiscal 1992.

The panel did approve $1.6 billion to continue research on the aircraft program, which calls for 75 bombers.

No B-2 proponent plans an amendment to restore the four planes to the budget and the House is expected to accept the committee's action.

The bill also would allow - but not require - the secretaries of the Navy and Air Force to assign women to fly Air Force, Navy and Marine Corps aircraft in combat. Currently, women are banned throughout the military from serving in direct combat roles.

The bill provides $2.4 billion for a third SSN-21 Seawolf attack submarine. Lawmakers from Connecticut and Rhode Island, home of the Electric Boat shipyard, succeeded in convincing the House to ensure competitive bidding on the contract for the third submarine. The vote was 235-157.

The amendment effectively negates a non-binding resolution the committee had adopted directing the Navy to award the submarine contract to Newport News shipyard in Virginia.

Electric Boat is building the first two Seawolfs.

The bill authorizes programs and sets spending ceilings. The actual money is provided in appropriations bills adopted separately. The Senate still must craft its version of the bill before the House and Senate meet in conference to iron out a final package.