Two FBI agents working in their California office and another agent attempting to arrest a fugitive in Cleveland were shot to death yesterday.

The unrelated incidents marked the first time in the FBI's 71-year-history that three agents had lost their lives in a single day. Before yesterday's killings, 23 other agents had died in the line of duty, 21 of them shootings.

FBI Director William H. Webster called reporters to the bureau's Washington headquarters to read a brief statement praising the three fallen agents, saying their service had been in "the finest tradition of the FBI."

"Their deaths are tragic losses and epitomize the sacrifices made by agents and their families on behalf of their fellow citizens," Webster said.

In El Centro, Calif., about 100 miles east of San Diego, agents Charles W. Elmore, 34, and J. Robert Porter, 44, had just begun work for the day when James Maloney, 30, a social worker walked in and shot both men with a 12-gauge shotgun.

Roger Young of the FBI's San Diego office said that Maloney, who had been under investigation in a case involving the misuse of thousands of dollars of public money, then killed himself with the shot gun.

There was considerable confusion about the Maloney incident at FBI headquarters last night, and one spokesman said the bureau would have no further comment until today.

But Young, in San Diego, was being quoted by United Press International as saying that "he went there with the express purpose of shooting and killing the agents."

It was further reported, by UPI, that Maloney had been an employe of the federal Comprehensive Employment Training Act program and that he had been a member of the radical Weatherman group during the early 1970s.

UPI said Maloney had gone to the FBI office with an appointment to talk to one of the agents about a request that he had made under the Freedom of Information Act for files regarding an investigation of him in the early 1970s.

Several hours earlier, agent Johnnie L. Oliver, 35, who began his career as a clerk at FBI headquarters, was gunned down in a Cleveland housing project during a search for a fugitive.

Oliver, armed with a shotgun, was shot in the chest as he burst into an apartment bedroom. He and five other agents were seeking Melvin B. Guyon, 19, who was wanted for kidnaping, rape and armed robbery in the Chicago area.

The shooting triggered a citywide manhunt for Guyon by hundreds of agents and policemen.

Earlier, as Oliver's sheet-draped body was removed from the building and placed in a van, a dozen or more teen-agers clapped and cheered. Police watched, grim-faced, in the 1,000-unit Carver Park housing project.

Cleveland FBI agent Anthony T. Riggio said the raiding party broke into the apartment through several entrances. He said Oliver was fired upon as soon as he announced he was an FBI agent.

Riggio said that as other agents rushed into the bedroom, a man believed to be Guyon, barefoot and shirtless and bleeding profusely from the chest, escaped through a window and fled on foot.

A housing project official said the apartment where the shooting occurred was rented by Guyon's mother, Catherine Little. The FBI declined to say how they knew the suspect was in the apartment.

Oliver joined the FBI in 1965 in Washington. He became a special agent, assigned to Philadelpha, in 1971. He was transferred to Cleveland a year later, and lived in suburban Strongsville with his wife and three children.

Police sources in El Centro said the FBI men there were working with Imperial County sheriff's deputies on a case involving large amounts of money, and that Maloney had been sought for questioning.

The sources said Maloney, a former radio disc jockey and more recently a community services worker in the federal CETA jobs program, left a suicide note with his estranged wife.

Porter, a 12-year veteran of the bureau, was married and had five children. Elmore, unmarried, had been an FBI agent for seven years.

Webster yesterday released statistics showing that 56 local, state and federal law enforcement officers were killed during the first six months of 1979, compared with 48 during the same period last year.

"The number of slayings remains high and the search for more effective methods to safeguard officers' lives must continue," he said.