WASHINGTON — Thousands of sexual assaults that occur in the United States every year are not reflected in the federal government’s yearly crime report because the report uses an archaic definition of rape that is far narrower than the definitions used by most police departments.

Many law enforcement officials and advocates for women say that this underreporting misleads the public about the prevalence of rape and results in fewer federal, state and local resources being devoted to catching rapists and helping rape victims. Rape crisis centers are among groups that cite the federal figures in applying for private and public financing.

“The public has the right to know about the prevalence of crime and violent crime in our communities, and we know that data drives practices, resources, policies and programs,” said Carol Tracy, executive director of the Women’s Law Project in Philadelphia, whose office has campaigned to get the F.B.I. to change its definition of sexual assault. “It’s critical that we strive to have accurate information about this.”

Ms. Tracy spoke Friday at a meeting in Washington, organized by the Police Executive Research Forum, that brought together police chiefs, sex-crime investigators, federal officials and advocates to discuss the limitations of the federal definition and the wider issue of local police departments’ not adequately investigating rape.