Top Virginia officials, including the commissioner of agriculture and two powerful General Assembly committees, today pressed Gov. Charles S. Robb to have the entire state declared a drought disaster area, citing crop losses that are expected to reach $235 million this season.

Later in the day, however, state Agriculture Commissioner S. Mason Carbaugh retreated from the recommendation, saying federal officials told him they would not accept such a sweeping declaration for the damage the dry summer has done to the nation's farms.

Projected losses by Virginia's farmers exceed the national average, with more than 70 percent of the state corn crop ruined, compared to 48 percent nationwide. Farms in Northern Virginia, especially cornfields in Faquier, Culpeper, Loudoun, Stafford, and Prince William counties, have been hard hit by the drought.

"We're going to speed up our applications" for federal disaster aid on a county-by-county basis, said Carbaugh. He said a statewide declaration by the governor would have reduced some of the paperwork needed to approve areas for low-interest loans, but said "you still have to justify it on a county-by-county basis."

A spokesman for Robb said the governor has not yet responded to a request from U.S. Sen. Paul S. Trible (R-Va.) this week for a statewide declaration. Carbaugh indicated that Robb would not make the request unless he is certain it will be approved in Washington.

"I thought maybe a little nudge from the state Senate's Agriculture Committee might help," said State Sen. Howard P. Anderson (D-Halifax), chairman of the committee, which joined its House counterpart for a joint four-hour hearing on the drought today.

Anderson said more than half of the state's approximately 80 farming jurisdictions have asked for disaster relief, and applications from other counties are arriving daily in the governor's office. In Maryland, all of the state's 23 counties have applied for disaster designations.

With a few rueful jokes about the first measurable rain in many weeks, the assembly committees, with Carbaugh and other state officials present, heard a succession of witnesses recount the effects of the drought.

"It's pure hell out there," said Dinwiddie farmer Billy Bain, who raises corn and soybeans on his farm south of Richmond. State Sen. Frank N. Nolen (D-Augusta), held aloft two ragged ears of corn that each cost "a penny to produce but won't bring one cent on the market."

Roie M. Godsey, state director of the federal Farmers Home Administration, said many Virginia farmers are still paying off low-interest loans received in the drought years of 1977 and 1980 and that many have reached their credit limit.

"We are bending and bending and bending as much as we can to keep these farmers in business," said Godsey. "We're just hoping for a miracle."

State Secretary of Commerce Betty J. Diener, Carbaugh's boss, was critical of federal programs, saying many of them have been cut under President Reagan. "There does not appear to be the federal relief on the way" available in previous years, she said.

For example, she said, state farmers participating in a new federal crop insurance program were expecting benefits of about $12 to $15 million.

However, a representative of the Federal Crop Insurance Corp. surprised state officials by announcing that the agency expects to pay out $50 million in benefits this year.

"They've updated their figures," Carbaugh said. "That's only a projection."

Carbaugh said later that the federal program is too restrictive and difficult to apply for because of arbitrarily imposed deadlines and benefit limits.

Del. J. Paul Councill Jr. (D-Southampton) said the state's problems are worse than they may seem. He said when the ripple effect of the drought is measured against livestock and businesses depending on agriculture, "I think we'll see a substantial increase in these figures."