Maryland's prisons chief ordered a Jessup prison put on lockdown yesterday after the fatal stabbing of a 26-year-old inmate - the latest in a series of violent assaults at the facility, including another fatal stabbing this year.

A lockdown means that the 1,200 inmates housed at the Maryland House of Correction Annex were largely confined to their cells and denied most privileges as authorities searched the prison for more hidden weapons.

Commissioner of Correction Frank C. Sizer Jr. said the Annex would remain on lockdown status indefinitely.

"Before we open it up again, we are going to have to have a better feel for what's going on out there, because we have an obligation to protect not only staff, but inmates as well," he said.

The stabbed inmate was serving a 30-year sentence for murder, attempted murder and weapons violations, according to George Gregory, a spokesman for the Division of Correction.

He would not identify the inmate yesterday, saying state officials had not yet been able to contact the victim's relatives.

The stabbing occurred about 10 a.m. in the prison's exercise yard, Gregory said. About 300 to 400 inmates were in the yard at the time, he said.

A correctional officer learned of the assault when the inmate staggered up to him, clutching his stomach where he had been stabbed, according to Gregory.

He was flown to Maryland Shock Trauma Center, where he died at 12:42 p.m., Gregory said.

The correction spokesman said that no weapon had been recovered or suspects identified as of late yesterday and that officials did not know what led to the stabbing.

The Annex is essentially a prison-within-a-prison - a separate, walled and razor-wired enclave inside the House of Correction compound at Jessup. The maximum-security prison houses many of Maryland's most violent prisoners, some of whom belong to prison gangs.

An inmate was stabbed to death at the Annex in January, and four stabbings on consecutive days in February led to a month-long lockdown at the facility so authorities could search for homemade knives and other weapons. Hours after the lockdown was lifted, another inmate was stabbed.

Union officials representing state correctional officers have blamed much of the recent violence at the Annex and other facilities on staff cuts.

But Sizer maintains that staffing levels have little to do with incidents like yesterday's stabbing.

He said that there were too few programs and jobs available to constructively engage the prison population - especially at a facility such as the Annex.

"Best practices tell you that if you are going to manage that kind of population, you have to keep them busy," Sizer said.

He said corrections officials had hoped to expand rehabilitative activities for inmates through an effort known as Project Restart, but that the department got legislative approval only to test the program at two prisons.

"If you are going to have a safe institution, you've got to have effective programming and activities for that population," Sizer said.

Yesterday's stabbing was the fourth homicide at state-run correctional facilities this year - which includes the strangling of an inmate on a prison bus and the recent beating death of a prisoner by correctional officers at the Central Booking and Intake Center in Baltimore.

Correction division officials said they asked state police to handle the investigation of yesterday's stabbing at the Annex because internal agency investigators were overloaded with other work.

The internal investigations unit of the Maryland Department of Public Safety and Correctional Services has been leading investigations of homicides involving state prison inmates. But that policy is set to change Oct. 1 because of a new law that Gov. Robert L. Ehrlich Jr. signed yesterday.

The legislation, sponsored by state Sen. Brian E. Frosh, a Montgomery County Democrat, requires that state police lead investigations of inmates who are killed inside or outside a correctional facility.

Frosh drafted the legislation in response to questions raised in articles published by The Sun last year. The articles focused on the death by asphyxiation of an inmate at a Western Maryland prison following a struggle with correctional officers. His death was ruled a homicide, but an internal investigation and a limited probe by an Allegany County grand jury found no wrongdoing by prison staff members.

Although the responsibility for homicide investigations will fall to state police, the public safety department's internal investigations unit remains in charge of investigating corrupt activities and violent incidents involving inmates.

Sun staff writer Gus G. Sentementes contributed to this article.