Maryland's U.S. attorney says he has made serious city crimes a priority - including drug and firearm violence - even as his office continues to come under attack from Baltimore's mayor for not prosecuting more city gun cases.

More than a third of all investigations launched this year by his office involve crimes committed in the city, U.S. Attorney Thomas M. DiBiagio said as he bluntly rejected Mayor Martin O'Malley's charges that federal prosecutors have contributed to Baltimore's endemic violent crime problem by pursuing fewer gun crimes.

DiBiagio said yesterday that he would "respond to him with indictments, convictions, sentencings," and pointed to a string of high-profile cases brought since January in connection with some of the city's worst violent crimes.

"If he would be willing to put aside his political motivations and join with us, I think we could get even more done," said DiBiagio, a Bush appointee who was sworn into office in mid-September and soon faced sharp criticism on the issue of gun crimes from the Democratic mayor.

Under DiBiagio, the U.S. attorney's office has brought charges that could carry the death penalty against a Baltimore man accused in three carjack slayings in August, and against the leaders of a drug gang believed responsible for a deadly shooting at a Memorial Day block party last year.

DiBiagio himself is prosecuting federal gun and drug charges against Eric D. Stennett, who was acquitted in state court of killing a city police officer and arrested this spring in a street-corner bust.

O'Malley, who is considering a run for governor as a tough-on-crime mayor, has said that he welcomes federal prosecutors' involvement in each of those cases. But that has not quieted his contention that more gun violations should be tried in federal court, where violators can face stiffer sentences with no possibility for parole.

Earlier this year, DiBiagio said he would pursue firearm cases in federal court only when defendants face a potentially longer sentence than they would in state court. He has acknowledged that would mean fewer federal gun cases.

The issue was reignited this week, as O'Malley shifted the focus to federal prosecutors in responding to statistics showing a significant decrease in the conviction rate in city courts for suspects charged in shootings and other felony gun crimes over the past two years.

While acknowledging that city police and prosecutors could do more, O'Malley also criticized what he called the federal government's "cowardly retreat from gun prosecutions."

In turning his attention to DiBiagio, O'Malley has for now muted his criticism of Patricia C. Jessamy, Baltimore's state's attorney. The Republican prosecutor is in many ways a more attractive target for O'Malley, who observers say got a cool reception from some in the black community after publicly criticizing Jessamy's efforts.

"I've noticed in the last year the cries of opposition have not been as steady, and, quite frankly, I think that the mayor's attack on her solidified her base," former state Sen. Larry Young said in a recent interview.

The effect of the mayor's attacks, DiBiagio said yesterday, is to alienate both of the city's top prosecutors. DiBiagio and Jessamy, meanwhile, have forged a tight partnership.

Former federal prosecutors say DiBiagio has charted a wise course in maintaining his independence amid political pressures from the city's popular mayor and his own political benefactor, U.S. Rep. Robert L. Ehrlich Jr., who also has long pushed for stepped-up federal gun prosecutions.

"From what I've seen, DiBiagio's office has taken on a couple of complicated, difficult, especially violent gun-related cases and has done so with what appears to be the encouragement and support of the Baltimore police and the state's attorney's office, who I notice are not complaining at all about what's happening," said Stephen H. Sachs, a Democrat who was appointed Maryland U.S. attorney in 1967.

Jervis S. Finney, a Republican who served as U.S. attorney in the mid-1970s, said that as the office pursues major violent crime figures, it will snare gun criminals as well. But he said the office cannot be expected to supplant state prosecutors.

"An element of the decision-making should be federal and state and local relations," Finney said. "But in my view, that doesn't go over to the feds saying, 'You're not doing it - we're going to do it.'"

Jerome E. Deise, a law professor at the University of Maryland School of Law, noted yesterday that just bumping a weak gun case to federal court does not guarantee a conviction.

In enumerating his office's caseload, DiBiagio said that a quarter - or 42 - of the 168 indictments brought in federal court in Baltimore since January involve firearm violations.

The bulk of those cases involve charges where felons were caught illegally carrying weapons. Several of the cases involve firearms used in drug trafficking or violent crimes or firearms used in killings.

DiBiagio also said that of the 259 cases he has authorized for investigation by federal prosecutors in Baltimore since January, 93 involve city crimes - 36 percent of the caseload.

The chief prosecutor said he did not have statistics for the same period last year, before he took office. O'Malley's office has asserted that federal firearm prosecutions have dropped about in half under DiBiagio, but the prosecutor said yesterday that he is focused on the quality of cases, not the numbers.

Sun staff writer Sarah Koenig contributed to this article.