The Senate last night approved and sent to the White House a long-overdue defense authorization bill for fiscal 1988 that through next fall sharply restricts testing of the president's space-based antimissile program and deployment of new strategic nuclear weapons.

The measure, which authorizes $16 billion less spending than the administration requested, reflects compromises worked out with the White House to avert an embarrassing veto confrontation over arms control between President Reagan and Congress before the president's Dec. 8-10 summit with Soviet leader Mikhail Gorbachev.

The agreement, achieved in a House-Senate conference earlier this week, won Senate approval, 86 to 9, after a desultory discussion that contrasted starkly with the heated debates over arms-control provisions that divided the Senate for most of the year.

The most vocal opposition came from Sen. Jesse Helms (R-N.C.), who said the arms-control provisions amounted to a victory for "unilateral disarmers" that would tie the president's hands in bargaining with Gorbachev, a charge denied by Republican and Democratic backers of the compromise. Minority Leader Robert J. Dole (R-Kan.), who spearheaded a summerlong GOP filibuster against stronger arms constraints, called it an "acceptable compromise."

The House approved the measure Wednesday, 264 to 158.

Senate Armed Services Committee Chairman Sam Nunn (D-Ga.) and ranking committee Republican John W. Warner (Va.) have said they expect Reagan to sign the bill. While there has been no official word from the White House, a senior official said earlier this week that it is "probable" that the president will sign.

The bill authorizes up to $296 billion for the fiscal year that started Oct. 1, compared with Reagan's $312 billion request, marking the third consecutive year Congress has held the military budget to a level that provides for no growth in military spending, if inflation is taken into account.

But the final figure hinges on current deficit-reduction negotiations and could be scaled back to $289 billion, a level that would force termination of at least two weapons programs, the Marines' Harrier vertical takeoff attack plane and the Navy's A6 bomber. Total failure of the budget negotiations between the White House and Congress could lead to deeper, automatic spending cuts.

Under the arms-control provisions, Congress would essentially hold Reagan through the end of his administration to a status-quo observance of the 1972 Antiballistic Missile (ABM) Treaty and the unratified 1979 SALT II treaty.

It would also continue the current ban on tests of antisatellite weapons against objects in space. But a House proposal to prohibit all but the smallest underground nuclear tests was dropped by the House-Senate negotiators who drafted the compromise.

To overcome White House objections, congressional negotiators dropped language passed by both houses that would have barred the administration from further exceeding weapons limits in the SALT II pact and would have banned antimissile Strategic Defense Initiative (SDI) testing that would violate restrictions under the traditional, or narrow, interpretation of the ABM agreement.

Instead, the administration would be required to dismantle a Poseidon nuclear missile submarine to assure that current weapons levels, already slightly above those mandated in SALT II, are kept through the current fiscal year. Also, the administration would have to limit SDI-related tests to those it previously outlined to Congress, all of which would fall within the narrow ABM interpretation. Spending on SDI research for next year was set at $3.9 billion, substantially below Reagan's $5.7 billion request but more than Congress was prepared to allow without the treaty protections.

While the treaty-related limitations are imposed through the Sept. 30 end of fiscal 1988, negotiators indicated they could be extended, modified or dropped, depending on progress in U.S.-Soviet negotiations and compliance efforts by the Soviets with respect to existing treaties.

In debate over the measure, Nunn said the arms-control agreement would "preserve Congress' power of the purse" in determining military expenditures while giving the administration "needed flexibility" in negotiations with the Soviets.

But Helms contended that the compromise was a "triumph of substance over form" for Reagan's foes, who prevailed by trading language for more meaningful funding restrictions.