D.C. police have a backlog of hundreds of unsolved homicide and rape cases that could benefit from DNA analysis, with the untested evidence sitting for years on shelves or stored in refrigerators at department buildings.

Testing the evidence could result in dozens of arrests in older cases if matches are found with DNA profiles of felons kept in national databases, investigators said. It also could help identify patterns, tying together seemingly unrelated crimes.

Although police routinely rely on DNA evidence in criminal investigations today, that was not the case as recently as a decade ago. Now the District is in the first stages of using the technology to solve older crimes.

Going through the old evidence is a major undertaking. Police officials said they are not sure how many cases in the department's massive Southeast Washington warehouse might contain DNA evidence. They made estimates based on the number of homicides and rapes in the past 20 years. More than 3,000 people have been slain and 2,500 people raped in the last decade alone.

"We have no idea what the scope of the problem is now, and we have been behind the eight ball for many, many years," said Detective Jim Trainum, who is at the center of the D.C. police department's DNA initiative. "We have gotten a late start."

Other departments across the country have launched major efforts to cull old cases for DNA. But D.C. police officials said they have fallen even further behind because they do not have their own laboratory to process the evidence.

D.C. police traditionally have relied on the FBI lab in Quantico. Although the FBI performs DNA tests for the District, police commanders said they did not want to overburden federal technicians with older cases when investigators needed quick results to solve more recent crimes. About half of the DNA evidence tested by the FBI lab comes from the D.C. police, federal officials said -- and that's without a crush of old cases.

"The FBI has a huge caseload of their own," said D.C. Police Chief Charles H. Ramsey. "They do not have enough resources to keep pace with our huge backlog."

Mayor Anthony A. Williams (D) has asked Congress for $9 million to help start building a state-of-the-art crime laboratory. Ramsey and others said the lab, which would cost an estimated $80 million, would help police comb through old cases more quickly and generate DNA profiles of potential suspects.

"DNA is the fingerprint of the 21st century," Ramsey said. "It is only going to get more and more sophisticated as time goes on. We need to keep pace with that. . . . A major police department, in a major city like ours, should have its own crime laboratory."

Sen. Mike DeWine (R-Ohio), chairman of the Senate Appropriations subcommittee on the District, has signaled his willingness to help the District but has not decided how sizable a contribution the federal government could make.

In the meantime, the department recently began to take some smaller, stopgap steps.

The city is hiring 10 new DNA technicians who will work and train at the FBI lab until the District gets its own facility. They should be at work in a few months, police officials said, giving the city more flexibility in sending DNA evidence for testing.

Trainum, a veteran investigator who helped solve a triple murder at a Starbucks coffee shop, heads a small group of unpaid interns who have spent the past two years delving through old homicide files. They hope to find evidence and witnesses that might help solve those killings.

Last week, the 15 interns began going through old rape cases, too.

With the help of anticipated federal grants, police eventually expect to comb through about 6,000 files looking for DNA evidence. Officials hope to submit about 130 homicide and rape cases to a private lab for DNA testing within the next year.

In a separate project, police technicians are reviewing physical evidence gathered from more than 500 rapes, which is stored in a refrigerator. About 200 of those crimes are unsolved, and the evidence has not been tested for DNA, officials said. Some cases probably will be tested.

Most of that evidence was taken from rapes committed in the past few years, after the department made changes in the way it stores evidence. Older rape cases could present problems: A 1997 report by an outside consultant said conditions at the department's evidence warehouse were so bad, biological material taken from rape victims might have been damaged.

Despite the recent activity, some outside the department criticized police officials for not acting more quickly on long-standing problems.

"It's a failure of leadership," said D.C. Council member Kathy Patterson (D-Ward 3), chairman of the Judiciary Committee. Patterson has been pushing the department to hire the DNA workers and has been a strong advocate of a crime lab.

Once technicians gather DNA evidence from a crime scene, they can develop a profile and enter it into state and national databases that contain DNA information on felons and suspects, and from evidence collected from other crimes.

Those databases can be used to link crimes to suspects. The FBI says more than 1.7 million DNA profiles are in its database. Most of those profiles -- about 1.68 million of them -- belong to felons whose DNA has been collected by officials in state prisons and jails.

Washington is not the only city with a backlog. About 350,000 rape and homicide cases are awaiting DNA testing across the country, the Justice Department says.

In New York, police began work in the late 1990s to eradicate a backlog of evidence from about 16,000 rape cases. Officials completed the $12 million project last year, according to Howard Safir, the city's former police commissioner, who started the effort.

"What happens more often than not, because of lack of resources, these things sit on shelves or in freezers in storage," Safir said.

In Baltimore, which has crime rates comparable to those in the District, police faced a similar challenge with more than 5,100 untested rape and homicide cases.

Since late 2001, Baltimore police have tested 1,600 cases and generated hundreds of DNA profiles. Police officials said the tests have generated more than 100 links between various crimes, or between crimes and offenders. Baltimore police have made arrests on old cases using DNA testing; however, they were unable to provide an exact number of arrests they made after a DNA "hit."

D.C. police investigators said that testing the agency's DNA backlog could help solve homicides such as that of Raymonde Plantiveau, 57, a French woman who was sexually assaulted and stabbed to death in her daughter's Northwest Washington home in 1983.

Police never developed enough evidence to charge anyone in the killing of Plantiveau, who was visiting her daughter on vacation. But they said they developed two potential suspects during the investigation.

For two decades, a potentially key piece of evidence -- the attacker's semen -- remained in a box in the Southeast Washington evidence warehouse. It was discovered recently during the review of homicide files by the department's unpaid interns. Police officials expect to submit the evidence for DNA testing in hopes it will identify Plantiveau's killer.

If the District gets a crime laboratory and makes major headway on the DNA project, Ramsey and other commanders will eventually have to confront a difficult question. The crime of rape has a statute of limitations of six years, and they must decide whether to test evidence older than that.

Some in the department are pushing for a massive round of DNA testing, saying that will help identify serial offenders. Others want to focus on those cases that can be prosecuted.

"There are different approaches that can be used, and we are exploring all of those based on the resources," said Cmdr. Christopher LoJacono, who heads the department's forensic division.

"Eventually, we would like to take all the old cases we have and put them into" a database, LoJacono said.