Howard L. Brooks leaves the courthouse after pleading guilty to lying to investigators about making payments to Sulaimon Brown. (Jahi Chikwendiu/WASHINGTON POST)

A campaign aide to Mayor Vincent C. Gray admitted to a federal judge Thursday that he was “instructed” to secretly pay a fringe candidate, known for his verbal attacks, to stay in the 2010 mayoral race.

Appearing in U.S. District Court in the District, Howard L. Brooks acknowledged that he gave money orders worth $2,810 to Sulaimon Brown, who first claimed last year that he accepted money and a job offer to harangue the incumbent, Adrian M. Fenty, in campaign forums.

Neither Brooks nor his attorney, Glenn F. Ivey, identified the person who gave the order to pay Brown. Prosecutors say in court documents that the instruction came during a June 2010 meeting involving Brooks, assistant campaign treasurer Thomas W. Gore and an unnamed “Person A.”

Brooks, 64, pleaded guilty to lying to federal investigators who were looking into Brown’s claims about a month after they first appeared in The Washington Post. Under a preliminary determination of federal sentencing guidelines, Brooks could face up to six months in prison but will be eligible for a sentence of probation only.

“Yes, your honor,” a bearded, blue-eyed and relaxed Brooks repeatedly told Judge Colleen Kollar-Kotelly as he admitted to the payments and entered the plea.

Brooks is the second Gray campaign figure to plead guilty to a federal charge this week. Gore, 56, admitted Tuesday to obstructing justice by shredding a notebook containing records of payments to Brown, as well as campaign-finance misdemeanors related to the payments themselves.

Brooks’s charge, making false statements, is less serious than Gore’s. He was also not charged with campaign-finance violations, although he acknowledged taking blank money orders worth $2,000 from Gore, signing them and giving them to the Gray campaign as his own — a “straw donation.”

People familiar with the investigation but not authorized to comment publicly confirmed that Brooks has cooperated with investigators, including wearing a recording device during conversations with Gore.

Ivey would not confirm that his client wore a device but said that Brooks had cooperated and will continue to cooperate “fully” with prosecutors. “Whatever they ask,” he said.

In a statement, U.S. Attorney Ronald C. Machen Jr. said that Brooks’s plea “further reveals the underhanded dealings that tainted the integrity of the 2010 mayoral campaign.”

Machen gave Brooks “some credit” for coming clean. “We urge others to do the same as we continue our efforts to get to the bottom of what happened during the 2010 election,” he said.

Charging documents indicate that Brooks initially lied to FBI agents in April 2011, telling them that he never gave “cash, money orders or other type of payments” when, in fact, he did.

Brooks admitted delivering three $500 money orders to Brown “on or about” Aug. 2, 2010. Brown told a D.C. Council committee last year that Brooks had given him two $500 money orders on that date, with instructions to “put the heat on Fenty” at a Ward 4 debate two days later.

Brown told the council panel that he had spoken directly to Gray at a restaurant after the debate and that Gray told him, “I think Howard has something for you.” Brooks, Brown testified, gave him money orders worth $500 and $150.

Prosecutors detailed money orders of $500 and $150 purchased by Brooks on Aug. 4, the day of the Ward 4 event, and delivered to Brown on Aug. 6.

Brown used the payments to fund his campaign and pay apparent personal expenses, including his Geico insurance bill, prosecutors said.

All told, Brooks is said to have bought, signed or otherwise handled $7,810 in money orders.

Besides the $2,000 straw donation and the payments to Brown, Brooks is said to have given a second $2,000 straw donation in the name of a friend. Campaign-finance records show a donation matching the description in court documents coming from a Brooks neighbor, Leroy Ellis, who also worked on the Gray campaign.

Brooks was a consultant to Gray’s campaign and transition teams, getting paid a combined $78,500 for unspecified work. Campaign workers and court documents have described him as being part of the campaign’s fundraising apparatus.

Before Brown’s allegations, Brooks was not a prominent or well-known figure in the campaign or in city politics generally. His appearance in Kollar-Kotelly’s courtroom Thursday afternoon was the first time many longtime political observers in the audience had laid eyes on him.

Brooks gave a brief interview to The Post for its initial story about Brown’s allegations. He denied making any payments and explained records of numerous phone calls with Brown by saying he had spoken to several rival candidates during the Gray campaign. Since then, Brooks has declined to comment publicly.

Gray has denied any knowledge of the payments, and prosecutors have not implicated him in the scheme outlined in the Gore and Brooks cases.

Brown alleged that Brooks acted in concert with campaign chairwoman Lorraine A. Green, a close confidante of Gray’s.

With two lower-level campaign aides now having admitted to the payoff scheme, eyes now turn to Green. She is a longtime friend of Brooks’s who is said to have brought him on to the Gray campaign and was associated with him in recent lottery dealings.

Two people familiar with the investigation said “Person A” is Green.

Green initially denied Brown’s claims, calling them “ridiculous.” She has remained silent since the allegations surfaced, but her attorney, Thomas C. Green, said this week that she had “cooperated completely with the investigation.”

Staff writers Nikita Stewart and Del Quentin Wilber contributed to this report.