A former security guard at the subdivision under construction in Southern Maryland that was devastated by arsonists in December pleaded guilty to a felony yesterday and, in exchange for leniency, agreed to cooperate with authorities investigating the fires.

Aaron L. Speed, whose trial was scheduled to begin next month, admitted that he was driven by anger toward his employer and resentment toward the affluent, educated homeowners who were moving into the Hunters Brooke subdivision.

Racial animosity, the confessed motive of the only other defendant to have pleaded guilty, was not mentioned during the proceeding. Many of the houses in the development were being bought by blacks; Speed and the other four defendants in the case are white.

According to a "statement of facts" signed by Speed, he helped to steal flammable liquids used to start the fires, encouraged a fellow security guard on duty that morning to leave early and participated in lighting the fires. The statement says that some of the material used by the arsonists was stashed at the subdivision when Speed was on duty several nights before the fires, concealed in drywall buckets and large plastic containers.

Speed, 21, also provided a hand-drawn map of the subdivision, identifying a house that was occupied so it would not be targeted during the arson, the document says.

Speed faces as much as 20 years in prison, and no less than five, for conspiracy to commit arson. The term prescribed by sentencing guidelines could vary dramatically depending on any past criminal record and on the degree of his cooperation with authorities, both sides said in court.

He also could be ordered to pay nearly $4.18 million in restitution, which he agreed was the amount of the financial loss attributable to his conduct.

In federal court yesterday, Speed stood and clasped his hands behind his back as he gave brief responses to questions from Judge Roger W. Titus. At one point, Titus asked how far he had gone in school.

"All the way to 12th grade, Your Honor, and then I dropped out," Speed said.

"You have stipulated to an amount of restitution that's an enormous number," Titus said later. "Do you understand that?"

"Yes, sir," Speed said.

Speed and five other men, ages 20 to 22, were arrested in rapid succession beginning 10 days after the pre-dawn fires Dec. 6 at the upscale subdivision in Indian Head, about 30 miles south of Washington. The fires, which fueled a perception that racial hostility persisted in Charles County, were the state's most extensive residential arsons in recent memory. The fires destroyed 12 largely unoccupied Colonial-style houses and damaged 15 others. Charges against one of the men have since been dropped.

Speed's plea agreement and the statement of facts describe his obligation to cooperate with prosecutors and the precise role Speed now says he played in the fires.

The document says Speed and others discussed carrying out the arson "according to a written plan prepared by" Patrick S. Walsh, a defendant previously described by prosecutors as the ringleader of the group.

"Speed participated in the arson . . . because he was angry with his employer, Security Services of America, for denying him bereavement leave after the death of his child," the document says. "He was also resentful about the wealth of the residents who he believed looked down at him and his own limited economic and educational status."

Investigators learned soon after the fires that Speed felt mistreated by his employer after the death of his infant son, a twin who succumbed to an illness. Prosecutors have said that some of the suspects referred to the arsons as "Operation Payback."

Speed's confessed motives differed from those of Jeremy D. Parady, who pleaded guilty in April. Parady said that the development was targeted because a large number of black people were buying houses there. According to a law enforcement affidavit unsealed earlier, Parady had told investigators that Walsh and Speed also set the fires for racial reasons.

Parady also pleaded guilty to conspiracy to commit arson. His plea agreement, which called for a prison term of nine years and 10 months, did not require him to testify against any other defendant. Titus delayed that scheduled sentencing last week, saying he needed to know more about Parady's role.

Speed's attorney, John Chamble, declined to comment yesterday. Speed is scheduled to be sentenced Oct. 18, as is Parady.

The other defendants, in addition to Walsh, are Michael M. Everhart and Roy T. McCann. Charges against Michael E. Gilbert were dropped without any public explanation by prosecutors.

According to law enforcement affidavits, all of the suspects but Walsh implicated others and, to varying degrees, incriminated themselves during interviews with investigators. In April, however, Titus threw out a written statement investigators took from Speed, saying that Speed was questioned improperly after invoking his right to counsel.

In that statement, Speed wrote that Parady had told him that he planned to set a fire behind a friend's house at Hunters Brooke. Arriving there, Speed wrote, "I seen JD [Parady], who told me he was playing a prank."

He didn't want to be involved, he wrote. "As I was leaving," he wrote, "I seen to my left a flickering of a fire."

Staff writer Joshua Partlow contributed to this report.

Aaron Speed worked as a security guard at the subdivision.The fires destroyed 12 largely unoccupied Colonial-style houses and damaged 15 others in the Hunters Brooke subdivision. Aaron L. Speed said he was motivated by anger and resentment to take part in the arsons.