Baltimore Mayor Martin O'Malley has settled on Prince George's County Del. Anthony G. Brown as his running mate in next year's race for governor and is likely to formally announce the selection Monday, said a source familiar with the mayor's plans.

O'Malley (D) said yesterday that he is close to making an offer to a lieutenant governor candidate, whom he did not name. But during an interview, O'Malley offered effusive praise for Brown, 44, a Harvard-educated lawyer and Army Reservist who recently returned from duty in Iraq.

"It would be an exciting team," O'Malley said of a pairing with Brown. "One of us has an administrative background, and one of us has a policy background. . . . It would be a really exciting opportunity for our state."

Brown, who is black and a second-term legislator from Mitchellville serving as majority whip in the House, would also add racial and geographic diversity to the ticket. Prince George's is home to more Democratic voters than any other jurisdiction in Maryland.

In a brief interview, Brown said he is "honored that the mayor would consider me as a running mate."

O'Malley campaign manager Jonathan Epstein declined to comment, citing the confidentiality of the process.

O'Malley, who is seeking to defeat Republican Gov. Robert L. Ehrlich Jr., has spoken with Brown extensively in recent days about how duties would be divided, according to those familiar with the discussions, who spoke on the condition of anonymity because the announcement has not been made. If the ticket is elected, Brown's focus will include issues related to higher education, economic development and health care.

The two have also talked about the importance of pushing a bold agenda in the first legislative session they would face, in 2007. Brown's ability to help with that task is part of what O'Malley finds appealing about him, sources said.

Aides to O'Malley's rival in the Democratic primary, Montgomery County Executive Douglas M. Duncan, say he, too, is considering a Prince George's lawmaker, Sen. Gwendolyn T. Britt, as a running mate. Other candidates, including some from the Baltimore area, are also under consideration.

Yesterday, Duncan and O'Malley sparred as they attended a conference in Baltimore on childhood lead poisoning.

Duncan, who has made education the centerpiece of his campaign for governor, told reporters he has "grave concern over the mayor's lack of interest in making education a priority."

"He's placed education last, as opposed to placing it first," Duncan said at a news conference called to tout the second of five installments on his "Education First" agenda.

O'Malley responded, "I find it sad that he would say that, given all the progress our kids have made."

Though Baltimore has the lowest test scores in the state, a majority of students in early grades have registered proficient scores on standardized tests in recent years.

O'Malley has limited control over Baltimore schools, but they have become a politically sensitive issue. The latest flare-up came Tuesday, when the State Board of Education voted to reject a city school system reform plan and directed the system to hire an outside monitor to oversee implementation of school system improvements.

Aides to O'Malley suggested that the vote was politically driven -- many of the board's members are appointed by Ehrlich -- and O'Malley said the state board's solution was not a smart use of money.

"I don't know that we need to hire another high-paid consultant to suck more money out of the classroom," O'Malley said.

Duncan's proposals yesterday included efforts to better promote the value of early childhood education, reduce class sizes and reduce the danger of lead poisoning and other health risks in schools and child-care centers.

The choice of a running mate is one of the more politically sensitive decisions facing O'Malley and Duncan.

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.

Del. Anthony G. Brown, "honored" to share a ballot with O'Malley.