B'nai B'rith is a terrorist organization that kidnaps children, Henry A. Kissinger is "a faggot," the International Monetary Fund is committing genocide, Walter F. Mondale is a KGB "agent of influence," and a Jewish spy for Britain helped assassinate Abraham Lincoln, but "he was not acting as a Jew."

Welcome to the unsettled world of Lyndon H. LaRouche Jr., the perennial presidential candidate who has spent much of the last 13 years making these and other scurrilous and totally unsupported allegations.

LaRouche, 63, is a political chameleon. In the 1960s he was a Marxist theoretician who lectured followers in Greenwich Village about economics. Now he is the leader of a worldwide sect with up to 1,000 members that lustily embraces many of President Reagan's programs, including the U.S. military buildup and the "Star Wars" missile defense system.

Two weeks ago LaRouche pulled perhaps his most unlikely outflanking movement. Two supporters won Democratic nominations for lieutenant governor and secretary of state of Illinois, prompting gubernatorial nominee Adlai E. Stevenson III to say that he would not run on the Democratic ticket with them.

The Illinois primary sent the national Democratic Party into a panic, although during the last few years the LaRouche organization has been sharpening its political skills and reaching a growing audience.

In the 1970s, LaRouche supporters ran for office under the banner of his U.S. Labor Party, but their electoral efforts did not take off until 1980, when they formed a new electoral arm, the National Democratic Policy Committee.

The group runs several hundred candidates a year. Some, at various times, have received 30 percent to 40 percent of the vote in congressional districts around the nation. They have won local seats and Democratic Party posts.

LaRouche's group has moved quickly to take advantage of the Illinois primary outcome, making available some articulate members to reporters and modifying its rhetoric as it seeks mainstream status.

But the movement is anything but mainstream and has been denounced from many quarters for years. LaRouche "leads what may be one of the strangest political groups in American history," the conservative Heritage Foundation said. "LaRouche has managed to attract a small but fanatical following to his conspiratorial view of the world."

The AFL-CIO said, "Mostly, he confounds people in various circles, but he also works hard to gain respectability out in front of his shadowy empire."

LaRouche runs his organization from a heavily guarded mansion on 170 acres in rural Loudoun County, Va. Two years ago, LaRouche moved his national headquarters, including hundreds of followers, from Manhattan to Leesburg, upsetting his new neighbors, who say they cannot understand his statements and are afraid of his bodyguards carrying semiautomatic weapons.

His people have been sinking roots in Leesburg, buying prime real estate, joining the Chamber of Commerce and starting a local newspaper with, among other folksy features, a gardening column.

It is a long journey from where he started.

Apparently rebelling against his New England Quaker background, LaRouche joined the Socialist Workers Party in the 1940s. By the late 1960s in New York, he had gathered around him a loyal group of a few hundred leftists. He took the name Lyn Marcus, and called his group the National Caucus of Labor Committees (NCLC). In 1968 it briefly took over a student strike at Columbia University, but was kicked out of the radical Students for a Democratic Society (SDS) for ideological differences.

Followers from that period describe him as a brilliant lecturer, although one found him "eccentric and odd."

Things started to change in 1973, when he ordered supporters to study karate and street-fighting. In December of that year, he announced that the Central Intelligence Agency had kidnaped a British follower and brainwashed him to assassinate LaRouche. In long and emotional sessions, LaRouche accused followers of disloyalty and berated them about their supposed sexual problems and political weaknesses.

During this period LaRouche also elaborated on the numerous supposed plots against him and humanity by a shifting pantheon of enemies. He has been constantly surrounded by armed guards since then, and today maintains that the KGB and the Libyans are after him.

The group went onto a kind of war footing in 1974, with many supporters quitting jobs and cutting family ties. The authoritarian atmosphere established then continues, fed by fear of imminent attack by evil outsiders, according to former LaRouche followers, experts on the group and published reports.

"It's a seven-day-a-week, 24-hour-a-day total immersion," said one dropout who, like others interviewed, declined to be identified for fear of retribution. "People wouldn't have any private lives any more . . . . Everyone's got to march to the same tune."

LaRouche and his supporters deny that the NCLC is a cult, saying he has no control over supporters.

By the mid-1970s, the group could be described less as Marxist than as conspiracy-minded, allying itself with neo-Nazi and extreme rightist individuals who shared its conspiratorial world view.

This was the period when LaRouche and his followers began making statements widely described as anti-Semitic. They said that Jewish bankers were behind the narcotics trade and questioned historical accounts of the Holocaust. An NCLC magazine said in 1978 that the B'nai B'rith "resurrects the tradition of the Jews who demanded the crucifixion of Christ."

LaRouche has said he is not anti-Semitic, but is anti-Zionist.

About six years ago, the group started toning down rhetoric and stepped up efforts to curry favor with active and retired law enforcement, military, CIA and other intelligence officials, as well as others in the federal government.

LaRouche followers try to talk their way into official meetings, where they promote policies of the Reagan administration and swap information with business and government leaders. Their "intelligence" comes from a worldwide network of followers that collects information on a range of issues.

Norman Bailey, a former economics staff member with the National Security Council, met with LaRouche followers numerous times while in government and said in 1984 that they had "excellent" international contacts. He described the LaRouche group as "one of the best private intelligence services in the world."

But some conservatives and intelligence community officials have raised the possibility that LaRouche's move from left to right is a fake. They think he remains in the Soviet camp, but with potential access to government secrets.

LaRouche associates and ex-members scoff at the suggestion.

About the only certainty is that LaRouche's supporters have followed their leader on an unpredictable ideological zigzag that can change week to week. One constant is the group's assertion that the world is in immediate danger of destruction -- nuclear disaster in 90 days, for example, or an acquired immune deficiency syndrome (AIDS) epidemic -- and that only LaRouche can save humanity.

The perception that LaRouche and the NCLC are under constant attack serves to make the group more cohesive and hostile, specialists on the group said. The siege atmosphere also makes LaRouche associates feel justified in their harsh attacks on critics, they said.

LaRouche supporters routinely use threats and questionable tactics to silence critics and former members, and to discourage the news media from reporting about the group, former associates said. The group's literature frequently alleges various critics are drug pushers, sexual deviants or psychopaths.

Dennis King, a New York journalist who has written several articles about LaRouche, said in court documents that his apartment building has been posted with flyers saying he is a homosexual and that he has received 500 abusive or hang-up calls at home.

LaRouche supporters deny allegations of harassment.

They also deny allegations of financial irregularities under investigation by a federal grand jury in Boston and by the Federal Election Commission.

Prosecutors in the U.S. attorney's office in Boston have said they are investigating "a massive pattern of credit-card fraud" and into possible federal income tax improprieties by persons and companies affiliated with LaRouche.

FEC documents show the agency is investigating allegations that LaRouche-affiliated groups borrowed money from individuals for LaRouche's 1984 presidential campaign, then failed to repay.

Lucille Pieper, a San Diego widow, alleged in a March 1985 complaint to the FEC that in 1983-84 she loaned $33,000 to a group for LaRouche's presidential campaign, "the savings of 37 years," and that the group did not repay her. In an interview, Pieper said that after the complaint was filed, the group started repaying her $340 a month.

Charles Dresow, a lawyer for the Los Angeles Labor Committee, said the probe is "part of a larger political foray" against LaRouche.

Meanwhile, LaRouche group literature campaigns against William Weld, the U.S. attorney in Boston. Its newspaper, New Solidarity, said he is corrupt, part of the drug underworld and "a Harvard punk."