As local government officials from throughout Virginia were descending on the State Capitol for an unprecedented lobbying effort for more state financial support, a General Assembly committee approved legislation that some supporters said could cost local governments as much as $15 million a year.

In what was a major victory for the state's electric utilities, the House Committee on Corporations, Insurance and Banking reversed itself and sent to the full House a measure that would led the State Corporation Commission set the rates that state and local governments must pay for electricity.

It approved by the full House and Senate, the measure would end the practice of letting Virginia governments negotiate with utilities over what price they pay for electricity, typically a rate well below that charged commercial customers.A close vote is expected in the House.

But the corporation commission and the utilities have long sought SCC control over the rates, claiming the present rate structure forces homeowners and commercial users to subsidize local government's use of electricity. The Virginia Municipal League and the Virginia Association of Counties have bitterly opposed the moves in both the courts and in the legislature, contending it would force new taxes on most localities to pay for the higher electricity costs.

One Fairfax County legislator said today he had been told the change would add about $1 million a year to the county's electric bill. Even so, the legislator, Del. Vincent F. Callahan Jr.(R-Fairfax), said he voted for the bill anyway, because he doubted the county's estimate.

"I think they pulled that figure out of the air," Callahan said after the committee voted 13 to 7 to report the bill. Callahan said he voted for the bill because it offered "equity" to all rate payers - "that's what boils down to."

The only other Northern Virginian on the 20-member committee, Del. Robert E. Harris (R-Fairfax), also voted for the measure.

Today's vote represented a switch of three votes from a Tuesday committee meeting when the committee voted 10 to 9, with Harris absent, to kill the bill. The committee then agreed, however, to reconsider the bill today, setting the stage for what some committee members said was intensive lobbying by utility and other lobbyists over the issue.

The measure had the support of the state attorney general's office and some consumer groups that were lured to it in what Del. Thomas W. Moss Jr. (D-Norfolk), an opponent of the bill, said today was "some vain hope" that it would prompt lower residential power bills.

The bill's sponsor, Del. Frank M. Slayton (D-Halifax), was careful today not to promise the committee that the measure might do anything other than possibly slow the rate of increase in residential electric bills. He argued that the measure would bring Virginia in line with an estimated 42 other states that let their state utility commissions set the rates local governments must pay for power service.

The bill's sponsors did agree to one major concession in an effort to move it out of the committee, directing that the SCC give the local governments a 15 per cent cut in their rate base under commercial rates because of the use of public rights-of-way for power transmission lines.

Prior to the energy crisis a few years ago, Virginia Electric and Power Co. had been charging some localities as little as one cent a kilowatt hour for electric service, well under Vepco's own costs. Vepco's residential rates start at 7.62 cents a kilowatt hour). The SCC ruled in 1972 that it had the power to set the rates, but the case was tossed out by the Virginia Supreme Court on an appeal by various local governments.

In other action today, the Virginia House gave initial approval to a study of "grade inflation" at the state's colleges by the Virginia Council on Higher Education. The measure's sponsor, Del. Carrington Williams (D-Fairfax), told the House his call for the study was prompted by news accounts of steadily rising grade averages at colleges around the country.

In its first break with the Senate during the current session, the House refused to agree to a Senate amendment that would delay until next Jan. 1 an amendment to the state's new right-turn-on-red law. The amendment would allow turns on red to the left on one-way streets. The House version would allow those turns after July 1.

The Senate will now either have to accede to the House version or the discrepancies will have to be worked out in a conference committee.