BUDAPEST -- As nationalist turmoil races across Eastern Europe, worried American executives and diplomats in Hungary are mounting a campaign against a prominent right-wing politician whose ideology has been compared to Nazism.

The aggressive lobbying effort aims to weaken support for Istvan Csurka, who has caused a political storm by publishing an 18,000-word manifesto that accuses Jews, Communists, liberals and the International Monetary Fund of forming an anti-Hungarian conspiracy.

The tract, which was published Aug. 20 in the newspaper of the Hungarian Democratic Forum, the dominant party in Hungary's center-right coalition government, is littered with apparently antisemitic, authoritarian and racist remarks.

Csurka is a vice president of the Hungarian Democratic Forum and leader of its populist faction. He wants to change the government's moderate course and take charge if Prime Minister Jozsef Antall, who has cancer, leaves the scene.

The American business and diplomatic community says it senses disaster if Csurka or his ideas triumph in Hungary, one of the few former Soviet Bloc states in East Europe that has not been swept up in nationalist hostilities. Hungary's prized political stability has helped it attract several billion dollars of foreign investment -- much of it American.

Csurka, a nationalist writer during the Communist era, is trying to capitalize on the country's hard times by saying the economic troubles result from what he calls a Jewish-led effort to suppress Hungary's post-Communist renaissance. Critics accuse him of seeking to tap the dark passions that led to the execution of 600,000 Hungarian Jews during World War II, when Hungary backed Nazi Germany.

Wall Street financier George Soros, a prominent Hungarian-American who has invested and donated heavily here, has sent a protest to Antall, who leads the Hungarian Democratic Forum. Soros, who is Jewish, was accused by Csurka of being a puppet of "Jerusalem."

The American Chamber of Commerce here is drafting its own protest to Antall, according to its president, Theodore Boone. The chamber's members -- who have steered clear of politics until now -- say Csurka is blackening Hungary's reputation and jeopardizing the investment environment.

"It's already a problem," said Boone, who heads the Budapest office of the Washington law firm Arnold & Porter. "There are formal and informal efforts to convey our concerns."

Antall issued a vague criticism of Csurka's manifesto last month. Diplomats say they believe that Antall, a masterful politician who prefers to move behind the scenes, opposes Csurka's ideology but is waiting for the right time to take action against a politician who may control enough votes in the National Assembly to topple the shaky coalition.

Hungarian-born U.S. Rep. Tom Lantos (D-Calif.) has issued a stream of harshly worded statements against Csurka and his supporters. Lantos has described Csurka's forces as "storm troopers of the new fascist movement in Hungary."

Behind the scenes, the Western diplomatic community is trying to prevent Csurka from gaining more legislative support than he already has. Diplomats are telling local politicians that Hungary, closer to Western-style prosperity than its East European neighbors, can lose everything it has gained in the last three years if nationalist passions spin out of control.

"We are letting every politician we come across at every level of the political class know that Csurka is a danger to the country, a real antisemite who is summoning up the demons of the past," a senior Western diplomat said.

Csurka's manifesto is a catalogue of ideas that opposition politicians and even some members of his own party view as rehashed Nazism. He accuses President Arpad Goncz of being under the control of "the Paris, New York and Tel Aviv" network, and he claims that Jewish Communists handed over power in 1989 to Jews in the banking community and opposition parties.

Goncz is not Jewish and was never a Communist. There are about 80,000 Jews in Hungary, which has a population of more than 10 million people, and they form the largest surviving Jewish community in Eastern Europe.

Csurka's manifesto blamed the "deterioration" in Hungary on "genetic reasons" -- seen here as a reference to the country's Gypsy and Jewish communities -- and called for whipping the media into shape so that it would "breathe together with the government."

While the Western campaign against Csurka could play into his hands by giving him a chance to charge that a new "Big Brother" is trying to meddle in Hungary's domestic affairs, diplomats say the risks are worthwhile because Hungary is an important and needed example that the transition from communism to capitalism can be accomplished without political instability.