Virginia's House of Delegates, in a slap at the powerful but much-criticized State Corporation Commission, voted today to expand the commission's membership from three to five despite opposition from the agency.

In a separate, consumer-related action, the delegates defeated a bill providing an auto emissions inspection program for Northern Virginia, but moments later changed their minds and approved the measure, which now goes to the Senate.

Some proponents of the SCC bill, which passed 57 to 41, said they hoped two new members would bring more consumer awareness to the commission, which has been under fire in recent years. Critics of the agency have charged that the SCC has been too soft in granting rate increases to Vepco, the C&P Telephone Co. and other utilities.

Others did not criticize the Scc, bu argued that its enormous powers -- it regulates banks, insurance companies, railroads and other corporations as well as utilities -- justified the expansion.

"Their work is much more complex than it once was," argued Del. Samuel Glasscock (D-Suffolk), in the brief House floor debate that preceded the bill's passage today. "Five good minds are a beter arrangement than three good minds."

The bill was denounced as a"a political move" by Del. William T. Wilson (D-Alleghany), who said the real need is to incease state spending for the SCC's research staff so it can better scrutinize claims made by utilities. "If you cannot improve the quality of the evidence before the (SCC) judges, it doesn't matter how many judges you have," he said.

The commission itself vehemently opposed the bill, which in three previous years was killed in the Corporations, Insurance and Banking Committee, long dominated by lawmakers friendly to the SCC. But this year, the committee's influential chariman, Del. A.L. Philpott (D-Henry) was elevated to speaker of the House and was forced to vacate the chairmanship.

"A.L.'s departure made a critical difference," said one delegate. "That bill would have never made it out if he d been there."

Delegates from Northern Virginia, where criticism of the SCC has been most intense voted 16 to 3 for the expansion, with Dels. Earl E. Bell (D- Loudoun), John S. Buckley (R-Fairfax) and John H. Rust Jr. (R-Fairfax) opposed.

Under the bill, the General Assembly would choose the new commisioners as it has chosen the old ones. The bill now goes to the state Senate, where opponents believe they will have little trouble killing it.

The controversial auto emmissions bill was first defeated amind grumbling by some delegaes about federal medling in Virginia's affairs, a popular theme here. The measure was revived however, after a Northern Virginia legislator reminded the House that failure to get in step with federal clean air rules could cost the state millions in federal funds.

"If we lose this bill, we're losing far too much," Del. Warren E. Barry (R-Fairfax) told his colleagues as he urged them to reconsider their defeat of the bill, which would require auto tailpipe emissions tests annually in Northern Virginia. Under the measure, cars flunking such tests would have to be repaired up to a maximum cost to the owner of $50.

Barry had voted against the bill at first, he said, as a protest against federal involvement in state affairs. "In many cases we can't legislate what's right or wrong for this state, but just go along with federally mandated programs," he said. "The feds are holding a big money club over our heads."

Sponsor Mary Marshall (D-Arlington) earlier pleaded with her colleagues to approve the measure -- which faced stiff opposition from automobile interests and was gutted in committee -- even though U.S. environmental officials have said it does not meet the standards of the federal Clean Air Act.

Admitting that the amended version of the bill "really is peposterous," Marshall said "the only reason to pass it is so the Senate can get it into shape." She said Sen Howard P. Andderson (D-Halifax), chairman of the Senate Agriculture, Conservation and Natural Resources Committee, had pledged to remove the House amendments.

The bill narrowly squeaked through committee last week after members voted to exempt Richmond-area drivers, cars more than five years old and air-cooled engines from the measure's purview.

Those amendments prompted a telegram from Environmental Protection Agency regional administrator Jack J. Schramm to Gov. John Dalton, warning that the bill in its present from was inadequate and that EPA had begun preliminary steps to freeze federal funds.

Marshall has warned that failure to comply with federal clean air rules would cost the state $250 million in pollution control funds and highway construction money. It also would trigger a federal crackdown on all proposed construction projects that would contribute to air pollution, focusing on highways and shopping centers.

Among the first projects to be knocked out if federal officials aren't satisfied with the state's effort, Marshall said, would be the proposed Dulles access road, the planned landscaping of i-66 in Rosslynn and $100 million worth of sewage projects in North Virginia.

Some 22 other jurisdictions, including Maryland and the District of Columbia, have adopted emissions control programs while Virginia and six other states so far have failed to comply. The jurisdictions were singled out because they show abnormally high levels of ozone contents in their atomospheres.

Del. James Dillard (R-Fairfax), who switched his vote from negative to positive on the measure, said he resented being forced to support a "garage man's welfare act" in order to secure continued federal funding.

"We ain't gotta like the bill," he said, "but, we gotta have it."