Elena Hernandez, 28, was shopping at an Arlington grocery store recently when a man approached her, flashed a fake badge and told her he was an immigration agent and that she was to come with him. Hernandez told police she was then beaten, raped and robbed. According to police, Hernandez (not her real name) and her alleged assailant are illegal aliens.

In the Adams-Morgan section of the District. police, responding to a report of a domestic quarrel, arrived to find a woman bruised and bloodied, her boyfriend gone. The woman refused to press charges and rejected all offers of medical help.

When questioned by police, she admitted she and her boyfriend were aliens and begged police to leave her alone. She told them his family has threatened to kill her if she says anything that results in his arrest or deportation.

Area law enforcement officers and Hispanic leaders say the two incidents represent merely a fraction of a largely unrecognized problem; crimes involving the area's growing population of illegal aliens from Latin American countries.

They are lured to Washington by the promise of Securing one of the thousands of law-paying service jobs and escaping the poverty of their homeland. Unofficial estimates put the number of aliens in the metropolitan area at 100,000.

Many live in the Adams-Morgan and Mount Pleasant sections of the District and in Silver Spring and Arlington officials say.

According to police in these communities, crimes involving aliens rarely come to their attention because the victims or witnesses fear deportation, are suspicious of police and believe that problems can best be handled in their own communities.

"The situation here is probably typical of many big cities around the country with large alien populations," said D.C. Police Officer Larry Moss who has worked in Adams-Morgan since 1973.

"Illegal aliens, if they even come in contact with the police, are extremely hesitant about giving out any information," Moss said. "Criminals who operate in the community have this haughty disdain. They taunt their victims because they are so sure crimes will never be reported."

Arlington detectives who investigated the assault on Hernandez say the case illustrates the problems of investigating crimes against aliens. One police officer with long experience in the Hispanic community said he believes fewer than 10 percent of crimes involving aliens are reported. Most of those that are reported involve domestic violence, consumer fraud, theft and rape, crimes generally committed by members of the Hispanic community against each other, officials say.

According to Arlington Det. Kenneth Adams, the Hernandez case is particularly unusual because the victim agreed to talk to police and testify against her alleged assailant. Hernandez agreed. Adams said, after repeated assurances that she would not be turned over to immigration authorities, an agreement approved in advance by an immigration official.

The incident occurred several months ago when Hernandez, a native of El Salvador who is employed as a maid and speaks no English, emerged from a food store on South Glebe Road carrying a bag of groceries.

"A man approached her and said he had been following her from another store," Adams said. "He showed her a fake ID and said he was an immigration agent and she was to come with him for a physical exam."

Adams said the two got into a car and drove to an apartment where two men were waiting. When Hernandez began to resist, Adams said, she was beaten and told to undress.

"She was told that if she didn't cooperate she'd be taken to immigration authorities in the nude." Adams said, Hernanadez was then raped at gunpoint and robbed of $3 and her groceries.

"The suspect then asked her for change so he could buy gas" to drive her back to the shopping center, Adams said. "His last words were, "If you report this to the police you'll be deported."

Arlington detectives were informed of the incident last month by Alexandria police who were conducting a related investigation.

Arlington police have obtained a warrant for the arrest of Carlos Husman 21, on charges of rape and abduction. Police say Husman, a former construction worker and waiter, is an alien from El Salvador and has been deported twice previously.

Hispanic leaders say that getting aliens to report crimes requires overcoming deeply ingrained fear and suspicion. In the minds of many aliens, they say, police and immigration officials are inextricably linked. Many aliens believe that any involvement with police is likely to result in their deportation.

When people in the community hear of an alien calling the police to report a robbery and then are turned over to immigration, that doesn't exactly encourage reporting of crimes," said Luis Rimbault, director of Ayuda, a Washington-based Hispanic legal aid program.

Officials of the U.S. Immigration and Naturalization Service say there is no legal requirement that aliens be turned over to them by local police. "It's entirely up to them," said INS district director Joseph P. Mongiello.

Area police say their primary concern is getting aliens to report crimes. "We want information about crimes like the rape and we don't care if people are legal or illegal," said an Arlington police spokesman. "We just want to get these criminals off the streets."

The situation has been made worse as some policemen have taken it up themselves to question foreign-appearing people about their immigration status.

"In the past some officers have asked for alien registration cards during minor confrontations where the alien, not knowing his rights, may have admitted he was illegal or simply may have been unable to produce the card," said Officer Wilson S. Barreto of the 3rd District police communicty center in Adams-Morgan. "Then they take them down to the station and call INS."

As an effort to end such practices-which are officially discouraged by the immigration service and which irritate the already-difficult task of investigating crimes against aliens-the District of Columbia Police Department issued a general order in November. It instructs officers to wait until a person has been booked for a crime before notifying the immigration service.

The U.S. Department of Justice also issued a statement in June requesting local and state police not to "stop and question, detain, arrest or place an 'immigration hold' on any persons not suspected of crime" solely because they are suspected of being illegal aliens.

Because language and cultural differences are also a source of constant friction between the police and the ethnic communities of Washington, D.C. police have put particular emphasis on recruiting more Hispanic and Spanish-speaking officers. Barreto, president of the Spanish American Police Association, said he expects as many as 20 new Hispanic officers to join the force in the next few months.