The hard-left of British politics - activists who want a Marxist revolution against Parliament and the crown - have launched a new campaign against the Labour opposition led by Michael Foot.
''Watch them,'' warns a close center-ground observer of British politics in an interview. ''They are dangerous - and they are undermining the recent truce agreement with Labour. It is a serious situation.''
It was the growing, grassroots power of the hard, Trotskyite left within the Labour Party that caused four former Labour cabinet members dramatically to leave the party to form the new Social Democratic Party.
Labour leader Foot began opposing the hard-left in public late last year. He patched up a truce agreement between himself and leading left-winger Tony Benn to try to present a united front.
Now that truce is in danger of breaking down. If it does, it once again would pit hard-left against moderate-left; threaten Mr. Foot's own position; and allow Social Democrats and Conservatives (Tories) to attack Labour anew as both divided and dangerous.
The new hard-left campaign has come in several steps:
1. An internal document of the Trotskyite group called the Militant Tendency (leaked in the Sunday Times) which contends that ''possibly one-third of the parliamentary Labour Party is no different in outlook, policy, and attitudes to the Social Democrats.''
The document criticizes Mr. Foot indirectly by criticizing ''vacillations and hesitations of the leadership of the Labour Party.''
The document outlines the standard Trotskyite recipe for revolution in Britain: Marxist ideas gain ground in the Labour party; a general strike leads to a left-wing Labour government; that in turn is undermined by conspiracies involving an anti-royalist coup.
2. An activists' letter in the publication ''Socialist Organiser'' advocating that parliamentary democracy be replaced with ''a higher form of democracy . . . The democracy of workers' councils, uniting legislative and executive powers.''
This follows a now-famous article by an aspiring candidate for Labour in Bermondsey, Peter Tatchell, which advocated confronting the government with activities outside Parliament. Mr. Foot, in a show of force long urged upon him by his moderate supporters, persuaded the Labour Party's National Executive Committee (NEC) to refuse to endorse Mr. Tatchell as a candidate.
Mr. Foot has also ordered an official inquiry into the hard left of the party.
3. Twenty-nine prospective Labour candidates (including Mr. Tatchell) issued a statement Feb. 22 specifically endorsing ''extra-Parliamentary action'' as an ''essential part of Labour strategy in and out of government.''
As a London ''Times'' editorial warned Feb. 23, activities outside parliament are permissible but not if they take the form of force. A number of political observers believe the hard left has force in mind.
The issue gains added importance because the hard left is nominating its own candidates for the general elections in two years time. The Labour National Executive Committee has now rejected Mr. Tatchell, and a new confrontation loomed as it considered this week whether or not to uphold a lower party committee's decision to endorse two more.
Mr. Foot was under strong pressure from his moderate parliamentary wing to reject both men. Late Feb. 24, the National Executive Committee endorsed one and rejected the other. The meeting was reported to have been accrimonious.
The fear of the moderate Labour Party is that with upward of three million people out of work and the number steadily rising, the appeal of the hard-left may grow - especially in northern England, Wales, Scotland, and Northern Ireland. In that case, the traditional Labour Party could lose hope of electoral success for years to come as Conservatives and the Social Democratic-Liberal alliance fight for the political center ground.