The execution of convicted murderer James D. Briley here last night marked a quickening pace of Virginia's use of the electric chair. Three other death-row inmates are scheduled to die in the next two months.

Briley's death brought to three the number of executions in Virginia since a 1977 U.S. Supreme Court ruling that allowed reinstatement of the death penalty. There are 27 inmates under sentence of death in Virginia prisons.

"It looks like we're just getting into the period where executions may occur more rapidly," said Jon Klein, a leader of Virginians Against the Death Penalty, a group that staged a quiet protest against the execution outside the Virginia Penitentiary last night.

"One thing it Briley's death has done is awaken more people. A bloodbath may occur shortly. It's unfortunate it may take this to fire up our side," Klein said.

Briley was pronounced dead at 11:07 p.m., a little more than six months after his brother Linwood was electrocuted in the same oak and metal chair.

The execution of James Briley, 28, convicted of killing a pregnant woman and her 5-year-old son, was carried out without incident as a crowd of about 400 death penalty supporters cheered outside the prison. Police separated them from the crowd of about 250 anti-death penalty demonstrators who softly sang hymns and held aloft candles.

"I think he should be electrocuted . . . because it was a pregnant mother and a baby," said Carolyn Jenkins, one of the few blacks among the supporters. "Let him feel what it is to die, let him feel what they felt."

Across a busy four-lane thoroughfare, a racially mixed crowd of roughly 250 people, who had been softly singing hymns to protest the execution, reacted to the announcement of Briley's death with a mixture of tears and anger. "This is terrible, really terrible," said one woman, looking across the road at the applauding supporters. "Talk about some civilized people."

James and Linwood Briley, who last May led a dramatic but short-lived escape of six death row inmates from the Mecklenburg Correctional Center, were part of a gang that law enforcement authorities had implicated in as many as 12 Richmond murders. A third brother, Anthony, is serving a sentence of life imprisonment.

The Virginians Against the Death Penalty protest group said there have been 42 executions in the nation since the Supreme Court ruling, including 10 this year. Florida leads the list with 11 and nearly 200 persons still on death row.

In Maryland, where there have been no executions since 1961 and none are scheduled, there are 18 on death row. There is no death penalty in the District of Columbia.

Kathi King, a spokeswoman for the Virginia State Penitentiary, said today that the state's next execution is set for May 2 in the case of Willie Lloyd Turner, convicted in February 1980 for the murder of a jeweler in Franklin, Va. during a robbery.

On May 15, inmate Michael M. Smith is scheduled to die for his 1977 conviction in the rape and murder of a York County woman.

And June 25 is the scheduled date for the execution of Morris Odell Mason, convicted in the 1978 rape and murder of a 71-year-old Northhampton County woman whose home was set on fire after she was bound to a chair inside.

Officials said the cases are in various stages of appeal and that some of the execution dates may change.

"Cases go through courts at different speeds. There's no way you can control that," said David Hathcock, spokesman for the state attorney general's office.