District corrections officials began the transfer of 456 inmates from the overcrowded D.C. Jail yesterday evening after jail inmates set fire to scores of mattresses, sending clouds of thick smoke through several of the jail's 18 cellblocks.

A jail guard and a D.C. firefighter suffered severe smoke inhalation in the fires, and both were listed in serious condition this morning at D.C. General Hospital.

Five other persons, three guards and two inmates, were treated at the hospital's emergency room for a variety of minor injuries and released, hospital spokesmen said. In addition, several other guards and inmates were treated at the jail infirmary for smoke inhalation, authorities said.

The jail, at 19th and D streets SE, was built to house 1,355 inmates, but has been severely overcrowded as its population in recent months has hovered at about 2,400.

Jail officials said a decision already had been made to move the 456 inmates to Lorton soon to ease overcrowding here, but that they began the transfers yesterday because of the fires and other recent jail disturbances. A jail spokesman said early today that about 200 inmates had been transferred by 2 a.m. and that plans called for a total of 283 to be shifted before dawn. The remaining 173 would be moved to Lorton beginning about 10 a.m. today, the spokesman said.

Corrections officials said that last night's lengthy transfer operation was complicated by the fact that jail guards also had to return to their cells more than 500 inmates who had been evacuated to the jail recreation yard because of the fires, and to process 70 inmates being bused back to the jail from city courts.

The fires started at 3:22 p.m. and burned about 45 minutes, according to fire officials. Smoke continued to pour through sections of the jail hours after all the fires had been put out.

More than 50 D.C. police officers, some clad in riot gear and some armed with shotguns, surrounded the jail as firefighters from more than 15 companies battled the fires. There were no escape attempts, jail officials said.

One of the first fires started in the Southwest 2 cellblock on the jail's second floor when a pile of mattresses and sheets outside the cells were ignited with matches, according to corrections officials. Smoke from the fire spread quickly to two other cellblocks on the second level, according to corrections spokesman Leroy Anderson. "You could hardly see," said jail guard Reginald Watson. "Smoke spread from one end of the unit to the other."

Anderson said inmates in the Southwest 3 cellblock on the third floor started a second fire in mattresses, but jail officials moved in and put it out before it had a chance to build.

Yesterday's incident was the second major disturbance at the jail in three days.

On Wednesday, inmates protesting conditions at the jail stormed a glassed-in guard's cage and burned paper, forcing the evacuation of about 80 prisoners into the courtyard. A five-hour standoff developed when prisoners refused initially to return to their cells. But the incident ended peacefully when corrections officials agreed to act on a series of inmate demands, including requests for more food, better medical attention and relief from overcrowding.

On Thursday, Kenneth Bynum, president of the union that represents jail guards, criticized corrections officials, asserting that they were responsible for the jail's overcrowding.

While fires flared inside the jail yesterday, dozens of inmates swarmed around air vents inside the facility and chanted in a muted chorus, "We want justice." In the recreation yard, evacuated inmates used hundreds of white towels to spell "HELP" in huge letters, apparently to attract the attention of media cameramen in aircraft overhead.

Last month, U.S. District Judge William B. Bryant threatened to hold D.C. Mayor Marion Barry and other city officials in contempt of court after he ruled that overcrowding at the jail had reached "crisis" levels.

Corrections director James F. Palmer said immediate transfer of inmates to Lorton was necessary to maintain security while debris at the jail was cleaned up, and to relieve overcrowding.

Last night, lines of inmates dressed in blue overalls streamed out of the jail to board buses taking them to Lorton. As they stepped from the jail, they put shopping bags and cardboard boxes filled with clothes and other personal belongings on flatbed trucks also bound for Lorton.

"It's truly a blessing," said one unidentified inmate, as he stood waiting to board a bus. "There's a lot more space at Lorton," he said, and "inmates won't be as hostile, no more."

The jail was intended primarily to hold people convicted of misdemeanors and defendants awaiting trial, while Lorton is the city's prison for inmates who have been convicted of serious offenses. However, Lorton, which has a capacity of 2,809, has also suffered from overcrowding, forcing an overflow of convicted people to be held in the D.C. jail while waiting for space to open up at Lorton.

The city has announced plans to spend more than $12 million in the next few years to expand the Lorton complex, which is located in southern Fairfax County, 20 miles southwest of Washington.

However, this has sparked strong protests from Northern Virginia politicians and residents who have long been upset about security and other problems at Lorton. They have tried for years to get the prison moved to D.C. or to have it scaled down.

Yesterday, John F. Herrity, chairman of the Fairfax County Board of Supervisors, protested the transfer of the 300 D.C. prisoners to Lorton and said the county would go to court to try to block the move. "We've got to put a stop to this sudden, abrupt transfer of terrorist operations from D.C. to Fairfax," Herrity said.