A Justice Department study yesterday estimated that nearly half the rapes from 1973 to 1982 went unreported, and an official suggested that victims do not come forward because they fear reprisal, public identification or "becoming entangled in an insensitive criminal justice system."

The report by the Bureau of Justice Statistics said random surveys conducted during the 10-year period showed that blacks were victimized more often than whites and a woman is twice as likely to be attacked by a stranger as by someone she knows.

The report said 40 percent of the estimated 479,000 women raped in the period did not report the crime and that 49 percent of the 1.03 million attempted rapes during the same period were unreported.

In addition, it is estimated that there were 123,000 male rape victims during the period, the bureau said.

The information comes from data collected annually. The bureau questions 123,000 people 12 years and older about their crime experience in the past year. Responses are used to estimate the number of rapes nationwide.

Assistant Attorney General Lois Haight Herrington, who heads the department's Office of Justice Programs, said, "Sexual-assault victims would be more likely to report the crime if they did not fear becoming entangled in the morass of an insenstive criminal justice system. In many states, rape victims must literally pay for their crime.

"They are given the bill for the medical exam required to gather physical evidence," she said. "Burglary victims are not charged for collecting fingerprints. Why should sexual-assault victims be charged for collecting evidence?"

Herrington said rape victims also may hesitate to come foward "knowing their addresses and phone numbers may be made public. They fear intimidation, threats and even reprisal from the defendant and his friends."

The average sentence for a rapist is nine to 10 years, but the actual time served less than three years in prison, she said.

Women who resisted their attackers managed to avoid rape in 73 percent of the cases, but 56 percent of those who submitted were victims of a rape, the study said.

About 15 percent of rapes and attempted rapes involved more than one rapist, the bureau said, and two-thirds of all rapes and attempted rapes occur at night, mostly between 6 p.m. and midnight.

Elizabeth Ozer, community education director at the Rape Crisis Center here, said she counsels women to avoid advice that says, " 'Don't fight back. Try to talk the guy out of it.' I think the more you wait, the greater danger you're in."