Allegations of sexual assault in the U.S. Army have climbed steadily over the past five years, and the problem has been abetted by weak prevention efforts, slow investigations, inadequate field reporting and poor managerial oversight, according to internal Army data and a new report from an Army task force.

The May 27 report, sparked by complaints from women's groups and female lawmakers about an apparent increase in reported assaults against U.S. servicewomen in Iraq and Afghanistan, states that the Army lacks "an overarching policy" for dealing with the problem, and that as a result it "does not have a clear picture of the sexual assault issue."

The report also states that the Army lacks a "comprehensive, progressive . . . program to train solders and leaders in the prevention of and response to sexual assault." It said commanders within the region covered by the military's Central Command have not always reported sexual offenses to Army investigators, even when they took action against those involved.

The Army's internal report echoes conclusions drawn in earlier, military-wide assessments. Data released separately by the Army Criminal Investigative Division made it clear that the number of sexual assault cases reported to the division increased each year from 1999 to 2003.

The numbers, released in response to a Freedom of Information Act request by The Washington Post, are the first year-to-year servicewide tallies on sexual assault cases provided to the public since 1998. They indicate that Army efforts to ameliorate the problem over the past five years have had little to no impact.

According to the data, the total number of reported cases of sexual assault involving Army personnel increased by 19 percent from 1999 to 2002 -- from 658 to 783, with annual increases ranging from 2 percent to 13 percent. During the same period, the number of reported rapes increased by 25 percent -- from 356 to 445, according to the data. The number of Army personnel on active duty, including reservists, rose during this period by less than 6 percent.

Between 2002 and 2003, according to the data, the number of reported sexual assault cases increased by an additional 5 percent and the number of rapes by 5 percent, but because of the war in Iraq, the number of Army personnel on active duty increased by 20 percent.

The Army acknowledges that these tallies probably understate the magnitude of the problem. Advocacy groups say that sexual assaults are routinely underreported, and that military victims are further inhibited by rules that bar confidentiality. A Defense Department report on the problem in May, based on visits to 21 military locations, provided data indicating rising sexual assaults from 2002 to 2003, which a Defense official said probably represented a fraction of the total in those years.

Army officials noted that the five-year tally included reports of abuse that proved to be "unfounded" after investigation, a number said to have tripled from 48 to 157 between 1999 and 2003. Army spokeswoman Lt. Col. Diane Battaglia said she could not explain why the number of cases deemed false had risen so much.

"The Criminal Investigation Division takes all reports of criminal behavior very seriously," she said.

Battaglia also noted that during the period covered by the data, the number of women on active duty in the Army increased. With more women in the Army Reserve than in the regular Army, and with more reservists on active duty, she said, "the raw number of sexual assaults being reported remains extremely low as a percentage."

The task force's report, to be released today at a hearing by a House Armed Services subcommittee looking into military sexual abuse, is the latest in a series of studies to find shortcomings in the military's policies and oversight. In its report last month, the Defense Department acknowledged that victims are inadequately supported and that investigations are often hampered by delays and manpower shortages.

That conclusion came after complaints in 2003 by female cadets at the Air Force Academy in Colorado that assault allegations had often been ignored and a report by the Defense Department's inspector general that one-fifth of the academy's women had reported experiencing at least an attempted sexual assault.

The Air Force and the Navy said they are still processing an April 8 request by The Post for data on the incidence of assault allegations across those services since 1999.

Although the Pentagon said it has initiated reforms, House Democrats led by Rep. Loretta Sanchez (Calif.) have been pushing for an update of sexual assault provisions in the Uniform Code of Military Justice, enacted by Congress in 1950. Their aim is to bring the code in line with a law adopted at the federal level and by 38 states, which expands the definition of sexual abuse and gives added protection for victims' rights.

After the Defense Department expressed its opposition, the Armed Services Committee rejected Sanchez's proposal in a straight party-line vote during its consideration in May of the annual defense authorization bill. "There are some basic flaws that haven't been addressed," Sanchez said in an interview.

Rep. Ellen Tauscher (D-Calif.), who requested today's oversight hearing, said "we're in this study phase," but without sufficient commitment to concrete reforms.