Prince George's County Del. Anthony G. Brown has emerged as the leading contender to become Baltimore Mayor Martin O'Malley's running mate in next year's race for governor, a selection that could be announced this month, several sources familiar with the process said.

Brown, a Harvard-educated African American lawyer and Army reservist who recently returned from Iraq, would add racial and geographic diversity to O'Malley's ticket if chosen as a candidate for lieutenant governor.

Prince George's is home to more Democratic voters than any other jurisdiction in Maryland. And with O'Malley and his rival, Montgomery County Executive Douglas M. Duncan, representing two other Democratic strongholds, Prince George's could prove key in the primary.

Duncan aides said he is considering several candidates in Prince George's and the Baltimore area.

O'Malley is still looking at candidates beyond Brown, said the sources, who spoke on the condition of anonymity because the selection process is continuing. But they said that Brown, O'Malley and their representatives have talked extensively about how responsibilities would be divided if they were elected.

In a brief interview yesterday, Brown, a second-term delegate from Mitchellville who serves as House majority whip, said he would consider the lieutenant governor slot if it were offered but said he is focusing on a possible run for attorney general.

In an interview earlier in the week, O'Malley said his campaign was in the midst of a "vetting process."

"We just want to make sure we pick and ask the right one and make sure that they have the benefit of the time to prepare for that sort of job," O'Malley said, adding that he has considered several strong candidates.

Campaign manager Jonathan Epstein declined to comment on those candidates or the timing of any decision, citing "the integrity and confidentiality of the process."

"I think he is close to a decision," former governor Harry R. Hughes (D), who has been assisting with O'Malley's search, said yesterday. He declined to elaborate.

The choice of a running mate is one of the most politically sensitive decisions facing O'Malley and Duncan in their bids to unseat Gov. Robert L. Ehrlich Jr. (R).

Blacks make up 28 percent of the population in Maryland -- the highest percentage of any state outside the Deep South -- and could account for 40 percent of the Democratic primary vote, party officials say.

Prince George's is home to about 19 percent of the state's Democratic voters, and both candidates have made several campaign trips to the jurisdiction.

In 2002, Ehrlich turned to Prince George's for running mate Michael S. Steele. With Steele seeking a U.S. Senate seat, Ehrlich could again draw from the county. Among the possible candidates are former county executive Wayne K. Curry and Adela M. Acosta, a former elementary school principal who is director of the governor's Office of Intergovernmental Relations.

Many black leaders felt alienated in the 2002 governor's race by Kathleen Kennedy Townsend's choice of retired Navy Adm. Charles Larson, a former Republican who is white.

"Some of us realize that might have been our downfall in 2002," said Del. Obie Patterson (D-Prince George's), who said he understood from people close to O'Malley that a decision on a running mate is likely to be announced this month or in early January.

A pick that early would be unusual, but the 2006 race has gotten off to an accelerated start. Duncan campaign manager Scott Arceneaux said Duncan, too, is likely to name a running mate before the Jan. 11 start of the legislative session.

Aides said Duncan is considering state Sen. Gwendolyn T. Britt (D-Prince George's), as well as Baltimore City Council member Keiffer J. Mitchell Jr. and Freeman A. Hrabowski III, president of the University of Maryland Baltimore County.

Campaign strategists for both Democrats said early running mate picks would allow the tickets to attend twice as many events and help raise money in an election in which Ehrlich could have a significant fundraising advantage.

But an early announcement would use up one of the few opportunities for guaranteed media coverage at a time when most voters are not paying attention, the strategists said.

Speculation about O'Malley's choice initially centered on Glenn F. Ivey, the chief prosecutor in Prince George's, but he recently announced that he would seek reelection next year.

In an interview yesterday, Ivey said Brown would be a "great choice" for O'Malley in part because of his legislative experience in Annapolis, which O'Malley lacks. "It's a good match that way, and it's a great match geographically," said Ivey, who said he has no direct knowledge of the process.

Del. Anthony G. Brown says he would consider joining a ticket.