U.S. Attorney Kenneth L. Wainstein is shaking up his homicide unit, creating an elite team of prosecutors not unlike the one in which he made a name for himself in the District during the late 1990s.

The changes are the most significant restructuring in years and come after a notable decline last year in the conviction rate in murder trials and complaints by judges about the performance of some prosecutors.

The conviction rate has rebounded and homicides overall have fallen, but the city has had a surge in killings of juveniles this year, and gun violence that has taken many of those young lives persists. In that climate, Wainstein said, the need for action remains.

In the new unit, to be led by Glenn Kirschner, a veteran assistant U.S. attorney, about 30 prosecutors will work exclusively on homicides. Other serious violent crimes, such as armed assault, will be handled by a new major crimes unit under Assistant U.S. Attorney Teresa Howie. The changes take effect tomorrow.

"I thought we could improve and refine what we're doing," Wainstein said. "Having a homicide section staffed by the most experienced and the most qualified prosecutors in the office is the best way to ensure that we will produce quality prosecutions in our homicide cases."

Wainstein said he has been considering changing how the office prosecutes homicides since taking over in May. Under the structure he inherited, homicides were assigned to a pool of several dozen prosecutors who handled a mix of criminal cases based on geography. Some of the lawyers had little experience with murder trials -- unlike those who will be on the team Wainstein is developing.

Preparing a murder case for trial is a major undertaking that can take months or even years. Prosecutors must prepare witnesses and track forensic and other evidence from the beginning of the grand jury process to the trial. Trials often are a challenge, especially in a city where witnesses frequently are uncooperative, prosecutors say.

While many cases tried by junior prosecutors end in convictions, they often demand much closer supervision, according to many prosecutors in the office. So-called "second chairs," once a rarity even in murder cases, have become common as supervisors seek to compensate for inexperience by adding a second lawyer to prosecution teams.

The reorganization was not driven by last year's disappointing numbers, Wainstein said. The conviction rate, which fell to 66 percent in 2003, is up to more than 80 percent this year, and Wainstein expressed pride in the work his prosecutors have done.

Wainstein, who prosecuted numerous high-profile cases in the late 1990s as an assistant U.S. attorney, was chief of staff to FBI Director Robert S. Mueller III when he became interim chief prosecutor this spring. Attorney General John D. Ashcroft made the selection after Roscoe C. Howard Jr. stepped down.

Wainstein's future in the job might depend on who wins the race for the White House. The president appoints U.S. attorneys, subject to Senate confirmation.

A few weeks ago, some prosecutors speculated that with the presidential election fast approaching and a major Justice Department review of the office due to begin next month, Wainstein might not have enough time to reorganize the homicide unit.

Wainstein, however, said he was determined to assign homicide prosecutions to a single unit and drop the decentralized system that has been in place for several years. D.C. police made a similar change more than two years ago.

Like some other top law enforcement officials, Wainstein thinks many homicides in the city are the work of a relatively small group of hard-core offenders.

A single homicide team, he said, would be better suited to targeting such criminals because its prosecutors would have the time and mandate to conduct the long, difficult grand jury investigations that often are necessary to make cases. That is especially true of older cases that have gone cold and demand much attention if they are to become viable, Wainstein said.

"There are a lot of unprosecuted, unclosed cases out there," Wainstein said. "There are a lot of grieving widows and mothers, friends, loved ones, who are starved for any progress on the case involving their loved one."

The last major reorganization was in 1999, when U.S. Attorney Wilma A. Lewis took the concept of "community prosecution" citywide. Teams of prosecutors were assigned to police districts, and they handled almost all cases in those geographic areas involving homicides and other violent crimes. The approach was envisioned as a way to build closer ties between prosecutors and citizens.

The community-based prosecution effort spread murder cases among several dozen lawyers, some of them with just a fraction of the trial experience once common among homicide prosecutors in the District.

Until several years ago, juries heard many misdemeanor trials, and by the time a junior prosecutor handled felonies, the lawyer had tried 20 or 30 jury cases. Now most misdemeanor trials are before judges, and that means young prosecutors don't work extensively with juries until they begin trying felonies.

Earlier this year, after prosecutors lost two straight murder cases tried before him, Judge Robert I. Richter voiced concerns about their performance to senior prosecutors.

Richter, who declined to comment, was not alone in his concerns. Other judges who handle homicide cases and other violent crime prosecutions in D.C. Superior Court also have been troubled, according to a judge who spoke on the condition of anonymity.

"There's a general feeling that there could be improvement" and that "basic trial skills" too often were lacking, the judge said.

Even as he addresses those issues, Wainstein is trying to sustain the community ties that have been forged in the past few years, he said. His memorandum announcing the changes emphasized that he thinks community prosecution has been a success and that elements of it will continue, even in violent crime prosecutions. Within the new homicide unit, prosecutors will continue to be assigned by specific police districts.

Eric H. Holder Jr., who as U.S. attorney in the mid-1990s launched a pilot community prosecution project, said that one of the questions was always how effective such a system could be in prosecuting crimes that require a significant amount of time and expertise.

Nonetheless, he said, the prosecutors working on such crimes as burglary, robbery and assault play an important role in collecting information essential to murder investigations, and the new homicide team should make sure it does not wall itself off from other prosecutors.

"The unit cannot be so separate that they become an office within an office," Holder said.