This is a story about the shadow world of American extremist politics.

It is a world of stretched and blurred definitions, of arcane political gamesmanship and Byzantine interconnections where the political right at times seems to merge with the left. It may not make sense.

But it demonstrates the huge and bizarre dimensions of American politics.

Begin with the National Caucus of Labor Committees, an obscure New York-based organization.

One of the most volatile and militant groups in the country, NCLC has until recently preached that it was on the verge of leading America to socialist revolution and smashing the "Rockefeller-Carter-CIA-controlled proto-fascist state."

In an abrupt switch late last year, it began to mute the talk of revolution and said it must now push instead for creation of an "industrial capitalist republic" under a "Whig" government with a 19th-century Hamiltonian banking system. The socialist state will apparently come later.

Meanwhile, NCLC is actively forging alliances with its erstwhile natural enemy - the American right. To wit:

Liberty Lobby, an ultraconservative group based in Washington, has advertised and sold copies of a 129-page report by NCLC describing what NCLC says is a "terrorist" apparatus of government agencies, private research groups and political organizations coordinated by the Carter administration, the Central Intelligence Agency and Rockefeller interests to "deindustrialize" American and go to war with the Soviet Union by 1978.

Spotlight, Liberty Lobby's newspaper, praised NCLC as "probably the only 'honest' Marxist group in the U.S. because it is not supported by Rockefeller money, as are all similar groups."

Lyndon H. LaRouche, 54, NCLC's leader and 1976 presidential candidate, has hired as his personal security adviser Mitchell L. WerBell III, an Atlanta-based firearms manufacturer and fervid anti-Communist who assisted Cuban strongman Fulgencio Batista until Fidel Castro's takeover in 1959. LaRouche claims he is an assassination target of the Maost "Baader-Meinhof" organization in West Germany and needs protection.

NCLC's political arm, the U.S. Labor Party, has joined several conservative groups and individuals including right-wing Republicans in court suits alleging 1976 presidential election irregularities in Wisconsin, Ohio, Pennsylvania and New York. The court actions have been largely unsuccessful so far.

The Federal Election Commission has called NCLC and Liberty Lobby on the carpet. It is checking the validity of NCLC's campaign contributors list and questioning Liberty Lobby about a Spotlight article suggesting that Jimmy Carter's campaign coffers were replenished by a Georgia-based drug/rock music promotion scheme. The two groups have publicly taken solace in their joint plight, accusing the FEC of Gestapo tactics to inhibit political activity outside the mainstream Democratic and Republican parties.

NCLC has been harshly critical of the "liberal" conservation and energy-saving policies of the Carter administration, blasting them as "antitechnology" austerity schemes calculated to return Western civilization t feudal serfdom.

Earlier this month, NCLC sent national committee member Jerry Rose to Memphis to sell its Hamiltonian national bank proposal to a conference of independent conservatives convened by a faction of the old segregationist American Independent Party of Alabama Gov. George C. Wallace. Conference leaders agreed to study the proposal.

NCLC, which claims to have its own elaborate intelligence-gathering network, has intensified its practice of criticizing other leftist organizations and on occasion has "briefed" local police departments and the FBI on planned leftist activity. It has also briefed aides to Rep. Larry McDonald (D-Ga.), a John Birch Society member who frequently publishes critical reports in the Congressional Record about what he says are violence-prone leftist groups, including NCLC.

In April, NCLC representatives met with the New Hampshire State Police to warn them that the antinuclear Clamshell Alliance demonstration planned at the Seabrook nuclear power plant site was a terrorist action concocted by the Rockefeller forces to foment violence. (No violence occurred during the May protest at which some 1,400 demonstrators were arrested.) An NCLC spokesman said at a press conference later that NCLC had relied in part for its assessment of the demonstration on an intelligence report called Information Digest, published by John H. Rees. Rees is a former D.C. police informant who now provides research assistance to McDonald on Capitol Hill.

NCLC's new alignment and rhetoric have left law enforcement authorities scratching their heads and fueled speculation among NCLC's conspiracy-minded competitors on the left - the Socialist Workers Party and the Communist Party, for example - that NCLC is aiding the police, the far right, big business - or all three.

Among right-wing activists who have been courted by NCLC, there is generally a cynical acceptance, a suspicion that NCLC is out to help itself and full knowledge of its origins in the Marxist-oriented Students for a Democratic Society.

"I don't think they've broken from their original SDS-Marxist roots," said John M. Couture, chairman of the conservative conference in Memphis, "and the supposition is that they're seeking coalescence [with the right] for short-term practical reasons."

In the Washington area, NCLC sought political and financial support last November from the campaign organization of John B. Burcham, an ultraconservative Republican candidate defeated by Democratic incumbent Gladys Spellman for Maryland's Fifth Congressional District seat. "We met with them and discussed the Whig kind of coalition we're trying to put together with Republicans all over the country," said Washington NCLC worker Susan Pennington. "We also asked them to support our (election irregularity) lawsuits in Ohio and Wisconsin," but nothing came of the meeting.

The FBI, which maintains extensive files on NCLC, including excerpts from Rees' Information Digest, describes NCLC in a memorandum as a "clandestinely oriented group of political schizophrenics who have a paranoid preoccupation with Nelson Rockefeller and the CIA." Another FBI memorandum obtained by The Washington Post calls NCLC a "violence-oriented Marxist revolutionary organization."

The New York-based group, estimated by various law enforcement agencies to have 700 to 1,000 hard-core members nationwide, is known for its militancy, authoritarian internal structure and the almost messianic zeal of its followers.

With unrelenting urgency, NCLC members preach two somewhat varying Rockefeller-CIA master plots: One, to destabilize society and trigger civil unrest by instigating labor strikes, hijackings, power blackouts and race riots to justify a police-state crackdown; the other, to deindustrialize society and convert workers into passive drones willing to do rote work by permissive use of marijuana and other drugs.

Officials of NCLC acknowledte their newly formed nexus with the right wing but say there is nothing mysterious or contradictory about it.

The right wing shares NCLC's suspicion of a Rockefeller-big money conspiracy, they say, as well as NCLC's opposition to decriminalization of marijuana and other "liberal" drug politics.

Paul Goldstein, NCLC's security and counterintelligence chief, said NCLC asked Liberty Lobby to plug NCLC's Carter "terrorism" report "because we wanted to get the word out as widely as possible."

The conventional daily press "was not going to do it," he said, "because, of course, they're controlled by the Rockefeller forces."

Willis Carto, treasurer of Liberty Lobby, said the lobby sold about 200 copies of the report and an accompanying index for $5 each during the 1976 presidential campaign. The lobby's Spotlight newspaper gave the report a favorable review in its Oct. 11, 1976, issue, warning only against "occasional distortions and omissions to be found in any Marxist-leaning polemic."

"It's not a matter of the right and the left getting together," said Goldstein. "Of course, there are basic differences, but in the framework of the anti-Carter, anti-Rockefeller, pro-nuclear technology issues, we're in agreement."

"We see eye to eye with them on that," echoed Carto.

Goldstein called Liberty Lobby a "patriotic force, although somewhat limited . . . You hear that they're right wing, that they're anti-Semitic, and there may be elements of that, but that's not what's important here."

Liberty Lobby, which has an extensive record of anti-Zionism, complained in its Spotlight review of the terrorism report, for example, that NCLC did not mention any of the "major Zionist groups, such as the notorious Anti-Defamation involved in the alleged Rockefeller-Carter terrorism apparatus.

WerBell, the tough-talking gun manufacturer and security adviser to NCLC's LaRocuhe, says NCLC hired him when it learned the radical Baader-Meinhof, or "Red Morning," organization planned to assassinate LaRouche during his current visit to West Germany. Persons identifying themselves as members of the Red Morning group claimed responsibility for the July 30 terrorist murder of prominent West German bank executive Juergen Ponto.

"Yeah, I know," said WerBell in a telephone interview from his suburban Atlanta home, "a lot of people say they [NCLC] are a bunch of Commies . . . I don't know what in the hell they are."

A former guerrilla operative for the Office of Strategic Services in World War II, WerBell said he agreed to take the LaRouche job irrespective of NCLC's politics because "if a guy's in danger, I bark like a Doberman. That's my job."

"Of NCLC, WerBell said, "Sometimes they're on the left. Sometimes they're on the right of Genghis Khan."

Officials at NCLC headquarters in New York deny subscribing to or receiving Information Digest, the biweekly intelligence report published by John Rees, but Boston NCLC representative Larry Sherman said his organization used it in assessing the planning antinuclear demonstration by the Clamshell Alliance at Seabrook, N.H., in May.

"We used Information Digest because we thought it was relevant, although we disassociate ourselves from it," Sherman said at a June 15 press conference in Concord, N.H., according to Associated Press reporter Kathryn Lorinczi.

New Hampshire State Police authorities acknowledge privately they received a copy of the Information Digest report in the mail but do not know who the sender was.

Rees, a former British newsman, denies sending the digest to either NCLC or the New Hampshire police but suggests that either could have received it indirectly from other Information Digest subscribers.

Rees mails the mimeographed intelligence report to numerous law enforcement officials, journalists, political researchers and others. Because of Rees' association with McDonald, leftists organizations view Information Digest as an instrument of the right, but it contains in-depth reports and analyses on the activities of both left-wing and right-wing organizations ranging from the Socialist Workers Party to the Ku Klux Flan.

Asked where NCLC fits into the political spectrum, Costas Axios, NCLC's chief of staff in New York, said:

"We are socialist, but first we must establish an industrial capitalist republic and rid this country of the Rockefeller anit-industrial, antitechnology, monetarist dictatorship of today."

Once the capitalist republic is established, Axios said, concurrent global economic development will occur, "and we will enter into a period of the highest prosperity the world has ever known."

With society expanding and material progress being made, "you win over the people's minds," he said, and under an advanced technology including fusion power, there "will be a trend" toward government of a socialist state.