Robert A. Sullivan, who spent more than 10 years on Florida's death row for conviction of killing the night manager of a Howard Johnson's restaurant, yesterday walked sobbing but unassisted to the state's electric chair and was executed with a 2-minute surge of 2,000 volts.

His head and lower right leg shaved, Sullivan sat in the three-legged oaken chair and read passages of the 62nd Psalm scribbled on a legal pad: "And in God alone is my soul at rest, because my hope comes from within," authorities at Florida State Prison at Starke said.

"To all my peers on death row, despite what is about to happen to me, do not quit," Sullivan said, according to prison spokesman Vernon Bradford. "I plead and encourage a continued effort to end this monster called capital punishment."

As two dozen witnesses watched, Sullivan's head was covered with a black hood. At 10:10 a.m., Florida Gov. Robert Graham told prison Superintendent Richard Dugger by telephone, "There are no stays. God save us all," according to Patrick Riordan, a spokesman for the governor.

One minute later, a black-hooded executioner unleashed the massive jolt of electricity. Sullivan was pronouned dead at 10:16 a.m.

A former Howard Johnson's restaurant manager, Sullivan, 36, became the ninth murderer in the United States to be executed since the Supreme Court lifted its ban on capital punishment in 1976. As the inmate with the longest tenure on death row in the nation, Sullivan was also the 199th convict to die since 1924 in Florida's electric chair.

The adopted son of a Harvard-educated surgeon, the 6-foot, 280-pound Sullivan battled for a legal reprieve until moments before his death, when the 11th U.S. Circuit Court of Appeals refused to delay it further.

On Tuesday night, the Supreme Court, by 7 to 2, also declined to spare Sullivan, noting in an unsigned opinion that "there must come an end to the process of consideration and reconsideration." That decision is believed to be another sign that a majority on the high court has grown impatient with the protracted legal maneuvers ensnarling capital punishment cases.

Despite a plea for mercy from Pope John Paul II, Graham also refused to spare the condemned man.

About 30 death penalty protesters kept a vigil outside the penitentiary walls yesterday morning, according to the Associated Press. They were flanked by several people supporting the execution. Groups opposing capital punishment were quick to deplore the execution of Sullivan, although none of those contacted predicted an accelerated pace as a result of yesterday's electrocution. As of Oct. 20, according to the NAACP Legal Defense Fund, there were 1,268 persons on death row in the United States.

"The death penalty is supposed to be reserved for the very worst of the cases," Stephen Bright, director of the Southern Prisoners Defense Committee in Atlanta, said. "But of the offenders, Sullivan is probably among the least deserving of execution. It's a classic example of the arbitrariness of the system."

Sullivan maintained his innocence until the end, claiming in an interview with the Florida Times-Union that he had been singled out because the state wanted to prove it could execute "middle-class white boys."

Last week, Roman Catholic Bishop John J. Snyder told the same newspaper that a Boston man had confessed to his priest that he was with Sullivan in a Miami gay bar at the time of the murder for which Sullivan was convicted. But the church was unable to provide further details about the witness because revealing details from the confessional is grounds for excommunication.

A college dropout who became manager of the Howard Johnson's restaurant in Homestead, Fla., Sullivan was sentenced to five years probation in August, 1972, for stealing $6,200 from his employer.

With a friend, Reid McClaughlin, Sullivan returned to the restaurant on the night of April 8, 1973, and killed night manager Donald Schmidt with a shotgun after robbing him, according to David Skipper, spokesman for the Florida Department of Corrections. Schmidt's watch and credit cards were found on Sullivan when he was arrested.

McClaughlin, who agreed to testify for the state against Sullivan, was sentenced to life imprisonment and was paroled in 1981, Skipper said. Sullivan was sentenced to die, and entered death row at Starke on Nov. 14, 1973. He came within 38 hours of execution in 1979 before a stay was issued, and yesterday's electrocution followed a 27-hour delay caused by legal skirmishing.

Defense attorneys argued unsuccessfully in their appeals that his trial lawyers failed to investigate Sullivan's alibi, that the system of administering a death penalty discriminates against those convicted of killing whites, and that Sullivan's sentence was not compared with those handed down in other murder cases.

At 6 a.m. yesterday, Sullivan was served a last meal of steak, french fries, milk and fresh strawberries.