Gov. Martin O'Malley's administration announced Thursday that it is withdrawing proposed regulations needed for executions to resume in Maryland, effectively extending a four-year moratorium on the death penalty.

Administration officials said the move was prompted by a U.S. company's recent decision to halt production of one of three drugs used for lethal injections in Maryland and many other states. The administration's proposed regulations specifically call for use of the drug, a powerful anesthetic known as sodium thiopental.

Rick Binetti, a spokesman for the Department of Public Safety and Correctional Services, said officials plan to submit new regulations to a legislative panel after reviewing a broad range of alternatives, including alteration of the state's use of a three-drug protocol.

"Putting a timetable on how long that will take is unrealistic at this point," Binetti said.

Lawmakers and others involved in the process suggested that a delay of six months could be possible. Maryland has five inmates on death row.

O'Malley (D), who opposes the death penalty, has been criticized by supporters of capital punishment for delays in implementing regulations called for by a 2006 court ruling.

Senate President Thomas V. Mike Miller Jr. (D-Calvert), a death-penalty supporter, said he considered the latest setback "very legitimate," however.

States across the country have been scrambling since last month, when Hospira of Lake Forest, Ill., announced that it would discontinue production of sodium thiopental, which it said it never condoned for lethal injections.

Shortages of the drug have prompted some states to switch to another controversial anesthetic, while others have sought to buy doses of sodium thiopental from foreign countries. Thirteen states recently asked the U.S. Justice Department for help in finding the drug.

"It is a broad problem that's still working its way through," said Richard C. Dieter, executive director of the Death Penalty Information Center in Washington. "You either try something new, or you look overseas or somewhere else.. . . Whichever way you go, you may run into problems."

Larry Traylor, a spokesman for the Virginia Department of Corrections, said officials there are "in the same situation, and we're investigating our options."

Traylor said Virginia officials have no executions scheduled and would resolve the issue before another takes place. The state has 10 prisoners on death row.

In Maryland - which last executed a prisoner in 2005 - corrections secretary Gary D. Maynard notified a legislative review panel of his department's decision to withdraw its regulations in a letter made public Thursday.

"Many states are now in the process of reviewing and revising their protocols in light of this development," Maynard wrote to the co-chairmen of the Joint Committee on Administrative, Executive and Legislative Review.

The panel plays an advisory role, and O'Malley could implement death penalty regulations over its objections. To date, his administration has been very deferential to concerns raised by the panel's co-chairmen, both of whom oppose the death penalty.

A hearing on the regulations that had been scheduled for next week was canceled after Thursday's announcement.

Sen. Paul G. Pinsky (D-Prince George's), a co-chairman of the panel, said he expects the department to take three to six months to draft new regulations.

"They're going to have to review this and figure out which chemicals to use," Pinsky said.

There has been a moratorium on capital punishment in Maryland since December 2006, the month before O'Malley took office, when the state's highest court ruled that new regulations were needed because the ones on the books had not been properly adopted.

For the first three years of his tenure, O'Malley unsuccessfully lobbied the legislature to abolish the death penalty rather than resume its use.

More recently, O'Malley has encouraged the review panel to act on the proposed regulations.

In 2009, seeking to compromise on the divisive issue, Maryland lawmakers tightened evidence standards required in death penalty cases. Capital cases are now limited to those that include at least one of three types of evidence: DNA or biological evidence, a videotaped confession or a videotape linking the suspect to the crime.

Still, the death penalty has continued to generate intense debate in Maryland.

On Thursday, a group of legislators and civic leaders announced a renewed effort to repeal capital punishment during the 90-day legislative session.

At a news conference, the group released the names of 21 senators and 61 delegates who are co-sponsoring the repeal bill - a larger number than in previous years.

O'Malley has not made a repeal bill a priority this year.

Miller and other lawmakers who support use of the death penalty have publicly urged O'Malley in recent months to implement regulations needed for executions to resume. And despite the moratorium, prosecutors have continued to seek the death penalty in some high-profile cases.

Last week, Prince George's State's Attorney Angela D. Alsobrooks said prosecutors would seek the death penalty against a Texas man accused of killing four people, including two young children, inside a squalid apartment in the Lanham area in August.

In an interview Thursday, Miller pointed to that case in arguing for the resumption of capital punishment as soon as the procedures can be worked out.

"Some crimes are just too terrible to allow people to continue to be subsidized by society," he said.