For the new arrival in the United States, almost every detail of his or her new life can be hopelessly confusing. Exotic change-giving machines must be mastered before boarding a computerized subway system and labyrinthine supermarkets charted. In some cases, following one's customs can lead to jail. Dozens of Latin women, for example, have suffered arrests for shoplifting unintentionally.

"When Latin women go shopping, they take along a big bag from home, fill it with what they want and empty it when they get to the counter so the cashier can tally the amount purchased," explained Karen McNally, a Montgomery County policewoman. "Well, if a security guard sees you doing that in this country, he'll arrest you for shoplifting."

To avoid this, and other embarrassments and confusion, for the past seven years McNally has been giving hour-and-a-half lessons on U.S. laws to Hispanic groups. From September to March every year, the county Board of Education's adult education division offers these sessions at local public schools.

Her talks also are part of a federally funded curriculum offered to new arrivals since last November by a Hispanic community center in Takoma Park. In addition to learning English, students are taught how to read want ads and how to determine work benefits. In the special case of Cuban refugees, they are taught things they never learned in socialist Cuba, such as writing checks, keeping accounts and comparison shopping.

The law education programs were McNally's own idea and she created the curriculum from her experience in working with the Latin communities' recurring problems. She says she knows of dozens of women who have suffered accidental arrest for shoplifting and many Latins who have complicated their legal situation by refusing to sign traffic tickets.

"The first thing Latins are told about the United States is that they should never sign their name to any piece of paper they can't understand," McNally explained. "So they don't."

In general, driving is fraught with problems. After much lobbying and delay, the State of Maryland has agreed to reinstate Spanish-language driving tests. Ten years ago, driving tests were given in nine languages in Maryland. Today, with a rapidly growing foreign population, the tests are given only in English. Many foreigners residing in Maryland solve the problem illegally by obtaining a license in the District of Columbia where the tests are given in Spanish.

When McNally, a friendly, energetic woman, arrives for a presentation at a Latin gathering, her first task is to overcome the foreigners' deeply ingrained fear of the police. Once she has explained that she is there to describe U.S. laws, and not to find out if her listeners are illegal immigrants, she is invariably a hit.

"For those of us who are here illegally, there is a lot of confusion between traffic and immigration police," a recent arrival says. "If we see a police car following us we start driving as fast as we can. Then they stop us for speeding and we run away because we'll be deported. By the time one of us is caught, he's really in problems. We're scared of the police."

McNally generally follows up the first session with an audiovisual presentation on sexual assault prevention, a subject which she has found is both deeply traumatic and taboo in the Latin community.

"The community has seen the interest she places in us," Jairo Castillo, a Salvadoran immigrant, said enthusiastically after a recent presentation. "We are all very grateful."

Cesar Reyes, a stocky, smiling man from Nicaragua, seemed to sum up the general view. "We thought the presentation was magnificent," he said. "But one thing bewilders us: She told us always to stay away from a criminal even if he is attacking the one we love. It seems that the individual who does an evil has more protection than the person who wants to stop him."

"Americans are very individualistic," a slim young woman from Bolivia added. "Our instinct is to help when someone is in trouble."

According to the best figures McNally was able to obtain from county officials, there are at least 1,200 registered Spanish-speaking voters and 31,000 Spanish-speaking legal aliens in Montgomery County.

Part of McNally's job is getting these people to understand U.S. law. The other part, as she sees it, is making her department aware of the needs of immigrants.

She acquired her knowledge of Latin culture as a high school student in a Catholic girls school in Mexico City, and then as a teacher in Puerto Rico in 1970. When McNally joined the police force in 1973, she naturally focused on the Hispanic community.

"There is a tendency among native-born Americans to think that immigrants should speak English and know the laws of this country from the moment they get off the plane," she said.

"A person caught in an emergency who dialed 911 for help and spoke only Spanish was out of luck until recently," McNally pointed out. "Crimes within the foreign community tend to go unreported--partly out of fear of the police, partly out of the inability to communicate."

Subtle and overt forms of discrimination can hit the newcomer in the United States where he or she least expects it. Because of problems with police who stopped foreigners and demanded their residence papers, a department directive warning against the practice was issued in 1979 by Montgomery County police. But some Hispanics say the arbitrary searches still occur.

"Officer McNally has helped us in many ways," Evert Diaz, from El Salvador, said. "She explains the law to us in her free time, but also she has fought to get better laws for us Hispanics."

"I hope these classes continue," Carlos Mijangos, another Salvadoran, said. "We come from radically different cultures and we need this information in order to adapt."