The Virginia Senate today approved the proposed merger between George Mason University and the unaccredited International School of Law in Arlington, thereby advancing the university's long-held hopes of acquiring its own law school.

The controversial measure passed the Senate by a vote of 28 to 9 and now faces an uncertain future in the House. There was no discussion of the merger legislation before today's vote, although the subject had been closely scrutinized before it was eventually voted out of a Senate committee last week.

Supporters of the bill, which has the backing of most of Northern Virginia's Assembly members, have said they expect the measure to be approved by the House Education Committee and then confront some opposition on the House floor.

The Virginia Council on Higher Education has recommended against the merger, but so far sponsors of the legislation have been able to convince Assembly members that Northern Virginia needs and deserves its own law school.

Meanwhile, a proposed constitutional amendment that would limit Virginia government spending to about 6.5 percent of state personal income received a surprising vote of approval in a House of Delegates Committee.

Many legislators had assumed that the House Privileges and Elections Committee, which passes on constitutional amendments, would relegate the controversial proposal to a study, as recommended yesterday by the taxwriting Finance Committee.

But the P and E Committee, responding to a persistent election year campaign by tax limitation advocates, voted 11 to 6 to send the proposal to the House floor.

Del. Mary A. Marshall (D-Arlington), one of three Northern Virginians who voted to report the amendment, said later, "Several of us voted for it because we wanted to have a vehicle to work with next year. We voted to keept it alive."

To become a part of the state constitution, a proposed amendment must be approved in two sessions of the General Assembly, with an election of members to the House falling between the Assembly votes.

The amendment reported today could become effective in 1981 and apply to the 1982-84 budget.If it is not approved this year, the earliest effective date for a spending limitation would be 1983, for use in the 1984-86 budget.

The P and E Committee also approved a bill, 15 to 2, requiring an advisory referendum in 1980 on ratification of the proposed Equal Rights Amendment to the U.S. Constitution.

The bill is sponsored by Del. Robert L. Thoburn (R-Fairfax), an ardent ERA opponent. Marshall, an equally ardent ERA advocate, said she regards the proposed referendum as a "delaying tactic."

The Virginia Senate has once rejected ratification of the ERA and the P and E Committee up to now has prevented a House vote on it. If the Assembly waits until after the results of the nonbinding referendum are known, it would have only two more opportunities to vote on ERA -- in 1981 and 1982 -- before the extended period for ratification by 38 states expires.

Marshall and Del. Richard R. G. Hobson (D-Alexandria), cast the only committee votes against the referendum. The committee once again rejected ratification of the ERA last week by a vote of 12 to 8. Chances for approval of the Thoburn bill on the House floor and in the Senate are uncertain.

Committee approval of the spending limitation proposal was a major victory for its chief patron, Del. S. Vance Wilkins Jr., a freshman Republican from Lynchburg.

A group of Lynchburg business leaders began developing the proposal long before California voters approved Proposition 13, but the California vote to put a ceiling on property taxes gave the Virginia movement the momentum apparent in today's committee action.

Gov. John N. Dalton expressed opposition to a constitutional spending limit in his annual address to the Assembly in January. Even if the proposal passes the House, an effort to assign it to a study commission is likely in the Senate.

In addition to Marshall, two other Northern Virginia delegates, Republican Vincent F. Callahan of Fairfax County and Democrat Earl E. Bell of Loudoun County, also voted to report the amendment.

The House and Senate each raced through passage of largely noncontrversial legislation today as each house neared a Wednesday deadline for action on bills introduced by its own members.

In the first hour of its deliberations, the House gave final approval to 72 bills and rejected only two. One of the defeated measures, sponsored by Del. David G. Brickley (D-Prince William), would have required foreign investors to register acquisitions of farm land in Virginia.

Dela. Ray L. Garland (R-Roanoke) and James B. Murray (D-Albemarle) argued strongly against the bill.

Garland, referring to other farm protests, called the fear of foreign investment a "Xenophobia that is merely the latest in a series of phobias that have animated the denizens of bucolia."