Thuy Nguyen of Arlington says she remembers being afraid the first time she wrote Rep. Frank R. Wolf (R-Va.), to ask his help in getting her mother out of Vietnam. Thuy, who left Vietnam days after the communists took over in 1975, said, "I'm not really smart about politics yet."

Impressed by Wolf's hard work on her mother's behalf, Thuy attended her first Republican Party meeting this year. Now the YMCA counselor is a member of Arlington County's Republican Committee.

"Mr. Frank Wolf, he's really concerned about our situation, the refugees," she says. "He's very sympathetic with our problems."

Wolf, running for reelection Nov. 6, may have plenty of sympathy for the refugees' problems, but he's also practicing good politics.

Democrats and Republicans in the Washington area are locked in a fierce battle for the votes of ethnic minorities, especially Asian Americans and Hispanics, the two fastest-growing ethnic groups regionally and nationally.

And in a potentially serious setback for the Democrats, historically the party that attracts immigrants, the Republicans appear ahead this fall, according to politicians and immigrant leaders. They appear to be winning handily among the Asians and to be fighting the Democrats to a virtual standoff among Hispanics -- a victory, because Hispanics have long been considered solidly Democratic.

The reason: The GOP has carefully targeted the most successful immigrant groups, appealing to many with flyers and literature printed in their native languages and often with a heavy dose of flag-waving, anticommunist rhetoric that appeals to many new citizens. Those appeals are welcomed by many immigrants from southeast Asia, eastern Europe and Cuba, Republicans note.

"We don't even see the Democrats coming to us and saying: 'We want you,' " said Mary Hay, a Vietnamese business consultant from McLean and a Republican activist. "The Republicans are really concerned about the minority people. They say: 'You're one of us.' "

Some compare the effort to win these new voters with the maneuvering of previous big-city Democratic machines for the votes of the Irish, Jews, Italians and other immigrants for the past century.

"It's an investment for the parties now," said Larry Sabato, a University of Virginia political science professor. "You get these immigrants early and make them indebted to you, and they, their children and their children's children will be loyal to you."

"These votes are still up for grabs, nationally and here," said Fairfax Supervisor Tom Davis, a Republican whose district includes thousands of Asians and Hispanics. "I don't think the partisan lines are drawn. All of them are swing votes, in my opinion."

Politicians would be foolish to ignore the new ethnics. There are approximately 100,000 Vietnamese, Cambodians, Laotians, Chinese, Japanese, Koreans and other Asians in the Washington area, as well as about 260,000 Salvadorans, Nicaraguans, Panamanians, Dominicans, Puerto Ricans and other Hispanics.

Most are not citizens, but political activists estimate that voter registration drives by the two parties and nonpartisan immigrant organizations have brought in from 25,000 to 30,000 new ethnic voters in the area during the past 18 months. The drive is part of a nationwide campaign that has seen the number of Hispanic voters grow from 3.2 million in 1980 to 4.6 million this year, a jump of more than 40 percent.

Politicians say the GOP is trying to attract the new ethnics in part because of its acknowledged failure to win black voters. The effort also coincides with the Republicans' drive to lock in ethnics, such as the Polish, Italian, and German Americans, who voted for President Reagan in 1980.

The Republicans, and particularly Reagan's reelection campaign, are wooing these voters with statements favoring such traditional values as law and order, patriotism, respect for family, school prayer and the entrepreneurial spirit.

Le Xuan Khoa, who heads a Washington clearinghouse on Indochinese-American affairs, said Vietnamese and Cambodians will vote Republican overwhelmingly because "they're very paranoid of communism. Maybe in the next generation, when it's clear to them the U.S. is strong, they'll open up more to the Democrats."

Barbara Hansberry, the Democratic National Committee's top Asian organizer, disputes that reasoning. She says for most Vietnamese, communism is "not a major issue. They're putting it in back of them . . . . They're more inclined to vote Democratic because of their financial situation. They're very interested in some of the social issues."

Hansberry was contradicted by many voters from Southeast Asia. "We're with the Republican Party for one reason -- the foreign policy," said Mary Chi Ray, a Vietnamese Republican leader from Annandale. "We're not economic refugees. Welfare and all these things are not our issue."

The Republicans also frequently show more grit and imagination in dealing with the new ethnics.

A Chinese American lawyer in Northern Virginia recalls that earlier this year, the Democrats telephoned him once to seek his support, and Republicans called six times. "They're still after me," says the lawyer, a Democrat. "That's how aggressive they are . . . . It's clearly a mistake on the part of the Democrats. They're waking up too late."

Republicans say it is among Hispanics that they are making their most dramatic gains. As recently as the mid-1970s, Latinos -- from Puerto Ricans in the Northeast to Mexican Americans in Texas and California -- voted about 90 percent Democratic. In 1980, Reagan won about 30 percent of the Hispanic vote. Now, GOP and private polls here and elsewhere show Reagan receiving almost 50 percent.

"They have a lot more money, and they're spending it," said Betty Baca, one of the Democratic National Committee's top Hispanic organizers. Baca said, however, that she expects most Hispanics will support the Democratic ticket because of the party's historical position on social issues.

The Republicans are concentrating on middle-class immigrants, and spending less time on poor ethnics, who are less likely to vote. Bill Lacy, the Republican National Committee's political director, said the GOP is acutely aware of class differences, and finds more fertile ground among the well-to-do.

Armando Lago, who heads the GOP's Hispanic voter campaign in Montgomery County, said he repeatedly sent squads of his 30 Spanish-speaking registrars to shopping centers in the county's working-class ethnic sections.

But they quickly learned that their efforts were more productive when they concentrated on wealthier Hispanics in Shady Grove and Bethesda. As a result, the GOP registered about 700 Hispanic voters in Montgomery County in the past three months alone, Republican officials said.

Republicans say they have all but written off Hispanics in such District neighborhoods as Adams-Morgan. Rafael Franchi, an Annandale economist who heads a group of 500 activist Hispanic Republicans in Northern Virginia, said that he disagrees with that decision, but that he agrees the GOP may never take hold among poor Latinos.

"There are two completely different Hispanic immigrations," said Franchi, who immigrated from Cuba in 1960. "One is looking for living off welfare checks and the other is looking for opportunity."

It is frequently more difficult to register Southeast Asians than other immigrants, say area politicans. The immigrants' experiences in their homelands have made them reluctant to get politically involved, even to put bumper stickers on their cars. They fear that support for a losing candidate will bring trouble to them from the winner. Many also fear that the Vietnamese government will punish their relatives back home if they participate in politics here.

"They've never had two parties," Hay says of the Vietnamese. "They have to be trained, to learn to adapt."

"They're a little shy," says Arlington GOP chief Helen Blackwell. "We're not sure how to approach them. Many are afraid of the government, and of the officials."

Both parties have set up nationwide telephone banks to call ethnic voters in the weeks before the Nov. 6 election and on election day. Most observers agree the Republicans have more sophisticated computer programs than the Democrats. They weed out ethnic names from residence listings and sort them by ethnicity so the party can send residents the right campaign literature. So far, the GOP has used the computers mostly in the heaviest ethnic battlegrounds, California and Texas, but the GOP's Lacy said they likely will be used in Northern Virginia districts by 1986.

Last May, 300 Asians were registered to vote at a GOP banquet and martial arts show at a Crystal City restaurant. Republicans also blanketed Virginia and Maryland Hispanics with mailings, and are advertising on Spanish-language radio.

These campaigns are reaching immigrant communities at a time when many new citizens are interested in becoming more Americanized, say local leaders of the Southeast Asian and Central American communities.

Dan Wong, a Taiwan-born engineer from Rockville attending an Asian GOP cocktail party in Arlington last month, said that his parents' generation devoted itself to hard work in this country, but that he and his friends are tired of the image of Asians as subservient workhorses.

"We seldom talk about which party we'll join," he said. "We talk about how we should get involved. We want to get into the action."