The Virginia Marine Resources Commission, at the urging of Gov. Charles S. Robb and Maryland officials, tentatively voted yesterday to extend an emergency ban on rockfish fishing to six months of the year statewide and toughen minimum size limitations.

The unanimous action by the seven-member commission came at a special meeting in Newport News called to ward off the threat of a federally imposed moratorium if Virginia failed to act to protect the endangered fish. A year-round statewide ban already is in effect in Maryland.

"We don't think it warrants putting people completely out of business," said Virginia Marine Resources Commissioner William A. Pruitt. "It's out of concern for the species as well as the fisherman that this recommendation is being made."

Under yesterday's decision, rockfish fishing would be prohibited in Virginia waters from Dec. 1 to May 31, which includes the period when the fish migrate into the Chesapeake Bay and spawn in the state's tributaries.

The commission also increased the minimum size limitation from 14 to 18 inches for rockfish caught in Virginia rivers and the state's portion of the Bay. The limit for rockfish caught offshore within the state's three-mile territorial limit would remain at 24 inches.

The regulation, which prohibits the taking, catching, possession, sale, transportation or processing of rockfish while the ban is in effect, must be aired at a public hearing and voted on again before it becomes permanent.

Virginia has been under pressure from federal authorities to reduce the state's rockfish catch by 55 percent or face U.S. sanctions. "We imposed [looser] restrictions in 1984 to get us toward that," said Jack G. Travelstead, assistant commissioner for fisheries management.

It was subsequently ruled that "what we did was not sufficient," Travelstead said.

He said the state's rockfish catch in the first quarter of this year "accelerated very rapidly" and totaled more than the catch for all of 1984. "It was obvious that some additional management needed to take place."

The rockfish, known elsewhere as striped bass, is popular with sport fishermen, but is not a major commercial fishery in Virginia compared, for instance, with flounder, according to Travelstead.

He said fewer than 100 commercial fishermen statewide in Virginia depend on rockfish for their livelihood. Commercial fishermen, however, have voiced repeated complaints about attempts to limit the catch.

Unlike those in Maryland, sport and commercial fishermen in Virginia would be allowed to resume rockfish fishing in June when the ban is lifted. Travelstead said the summer months are very slow, but that the rockfish catch picks up again in September.