Gov. Gerald L. Baliles, battling to save his far-reaching proposal to change the way Virginia pays for its transportation needs, today attacked the members of his own study commission who have criticized his plans.

"We can't raise the gas tax high enough to produce the billion-dollar-a-year program that we need," Baliles said in a speech delivered here to the AgExport 1986 Forum, but clearly aimed at a wider audience.

Earlier this week, the finance subcommittee of the governor's Commission on Transportation in the 21st Century refused to adopt key provisions of Baliles' plan that would reduce the state's dependency on gasoline taxes to finance transportation programs.

The governor recommended establishing a separate trust fund for new construction and expansion of the use of bonds. Baliles said separate funds are needed for road construction and maintenance because the existing single-fund formula gives priority to maintenance at the expense of road construction. As a result, 57 percent of all gasoline tax revenue is funneled into repair work.

At stake is an estimated $10.2 billion in highway needs throughout the state in the next 10 years. Much of that money would be used in Northern Virginia, including construction of a Springfield bypass, widening Rte. 28 in Loudoun and Fairfax counties and Rte. 234 in Prince William County, planning for a part of an outer beltway in Northern Virginia and improving scores of primary and secondary roads in the outer suburbs of Northern Virginia.

The cost of the state's highway needs is escalating at a time when the federal government is sharply curtailing its contributions to highways and mass transit. Federal contributions to Virginia could be cut by as much as 17 percent next year, officials said.

Virginia now spends about $400 million a year on highway construction, two-thirds of which is federal money. With a $1 billion annual need, Baliles said, "That means we must raise $500 million to $700 million in new money.

"We should not shrink from consideration of the new. The approach of the past is simply wrong for the future; it forces us to be preoccupied with what we cannot do, instead of what we can do."

Baliles said long-range plans are necessary to "break the cycle of a quick-fix every four years."

He said the next few weeks are "a very critical period" for the commission, which has an Aug. 1 deadline for making recommendations to a special session of the General Assembly in September.

Baliles said he and his advisers, including Transportation Secretary Vivian Watts of Fairfax, are working to reverse the recommendations of the finance subcommittee, headed by House Speaker A.L. Philpott (D-Henry), before the full commission's next to last meeting Monday.

Baliles called for "a combination of bond options." He said that includes revenue bonds, which require specific pledges for repayment, such as the use of tolls; moral obligation bonds, which would carry a limit imposed by the legislature, and general obligation bonds for specific projects, which require voter approval