A 21-year-old D.C. Jail inmate has been hospitalized in critical condition since Monday, when he tried to hang himself in the jail infirmary in an incident that officials acknowledge was made possible in part by overcrowded jail conditions.

Thomas C. Lyle, who is charged with the June 30 rape of a Northwest Washington woman, had been transferred to the infirmary last Friday and placed under a suicide watch after a jail psychologist found that he was a suicide risk, said Jesse Jones, the jail's administrator.

Lawyers with the D.C. Public Defender Service who initially represented Lyle said he was able to attempt suicide even under those conditions because of inadequate supervision by jail personnel, which they contend is a result of overcrowding of inmates and understaffing.

Jones said a preliminary internal report found there was no negligence by jail employes, adding that suicide attempts are hard to stop because of the jail's extreme overcrowding.

"We're not staffed to the point of constant one-on-one supervision," Jones said. "All a suicidal inmate would need was three minutes, and you can't expect an officer to check in every three minutes . . . . Sometimes you turn your back."

Lyle, who moved here from Georgia a month ago, is "virtually brain dead" at D.C. General Hospital and is "not expected to live," according to a document his lawyer filed in D.C. Superior Court earlier this week. Hospital officials said late yesterday Lyle's condition remains critical.

A prison officer found Lyle hanging from a bedsheet in his cell in the jail's third-floor infirmary about 12:10 a.m. Monday, jail officials said.

Jones said jail staff members had "acted expeditiously" in placing Lyle in the infirmary after the psychologist found that Lyle might try to take his life.

Jones, who has worked at the jail for eight weeks, said he does not know jail policy on dealing with suicide risks, but said that jail officers check in frequently with such inmates. "We don't take such warnings lightly."

It could not be learned how frequently officers checked in with Lyle Sunday night. Jail officers interviewed said that, given what they view as understaffing at the jail, it is easy for inmates to attempt suicide.

"If I have four or five people on suicide watch, I may not be able to check on them all," said Sylvia Hall, a D.C. Jail officer and chief shop steward for Local 1550 of the American Federation of Government Employees. "We're really understaffed."

Two officers are assigned to the 23-cell infirmary on the night shift, compared to four officers and a number of doctors and nurses during the day, Hall said.

Officers are supposed to check in about every 20 minutes with most inmates, and every five or 10 minutes with suicide risks, she said, but understaffing often makes that impossible.

"This case is a result of the number of inmates and employes here in the jail," said a jail official who declined to be quoted by name. "We're not able to handle things here, with the overcrowding. It's chaos."

"Supervision is inadequate" at the jail's 24-bed infirmary, said Tony Fitch, deputy director of the Public Defender Service, which represented Lyle until yesterday. "There are very substantial problems at the jail, and it's part and parcel of the overcrowding . . . . This is of the gravest concern to us."

U.S. District Court Senior Judge William B. Bryant ruled last week that city officials are in violation of the strict conditions he set last year in a decision allowing two inmates per cell. More than 2,400 inmates are housed at the jail, designed to house 1,355 prisoners.

Lyle, who worked for the last month as a janitor, was arrested and charged with rape June 30, police said.

An assailant entered the victim's Northwest home through a back door about 6 a.m. that day and beat and raped her, according to court documents.

Lyle was arrested in the house a short time afterward, the documents said.

Hours later, at police headquarters downtown, detectives noticed that Lyle was acting strangely, said Capt. John Collins of the sex squad.

"He kept asking how much time he'd have to do in jail," Collins said. "He couldn't take it. He kept shaking his head. He appeared to detectives to be despondent."

Collins said he notified jail officials on Friday that they should pay special attention to Lyle because he might be suicidal.

At a hearing later the same day, Commissioner Joseph Sitnick set bond for Lyle at $5,000. A representative of the U.S. attorney's office said during the bond hearing that Lyle had been acting strangely while in custody.

Conferring with Lyle's family, public defender Allie Sheffield said, she learned that recently, while he was living in a small town near Athens, Ga., Lyle had been deeply depressed. He had not been hospitalized for his mental condition and had no arrest record, Sheffield said.

Sheffield said she asked court officials to arrange for a jail psychologist to examine Lyle.

Lyle's family members declined comment, referring calls to Robert Muse, a lawyer they have retained in the case. Muse also declined comment, except to say that jail officials have declined to inform him of the results of the jail's preliminary investigation.

Yesterday, Sitnick vacated his earlier order that Lyle be held on $5,000 bond, and said he could be released on his personal recognizance.

"He's dying and his family wants to be with him," Sheffield said. ". . . . He's a very attractive, nice-looking young man . . . . This is just pitiful."