Militant Tendency -- a Marxist thorn in Michael Foot's Labour Party

A square-jawed printer from Liverpool, Tony Mulhearn is vehement in his adherence to a Marxist Britain - no monarchy, no NATO, no nuclear weapons, wholesale nationalization.

* Quick-spoken intellectual Peter Taafe edits a weekly publication that bills itself ''the Marxist paper for Labour and youth,'' and the source of whose finances remains something of a mystery.

* Young, sports-coated with a short red beard, Dave Nellish is the prospective Labour Party candidate for Parliament from an area of Coventry. Among other things, he believes Labour members of Parliament should live on a worker's wage and turn the excess back to the party.

At first glance, these three seem an unlikely trio to hit the front pages and the television screens of Britain over the past two years and still today. Britain is and remains a staunchly centrist country.

It seems even less likely that they could be of direct interest to the White House, the State Depaartment, or the Pentagon in Washington.

Yet these three men, and about 60 to 80 other young Marxist activists, have gained a public image and an importance beyond their ideas and their numbers.

All are members of the Militant Tendency, a small but highly organized group of Labour Party members on the far-left, Trotskyite edge of the political spectrum. The Tendency is an offshoot of the Revolutionary Socialist League, founded by a communist called Ted Grant, who came to Britain from South Africa in the 1930s.

Brian Crozier, a writer and analyst of subversive groups, estimates some 2, 000 members in all, and 80 full-time activist workers. In 1979, every member had to contribute an estimated (STR)2 ($3.38) per week, for an annual income of more than (STR)200,000 ($338,000). Sources in Blackpool indicated that the levy is now more than (STR)5 a week, even for the unemployed, and yields an income of half a million pounds a year.

Although its political aims seem wildly optimistic, the Tendency has won considerable pockets of power at the party grass roots. It has seized a measure of power over party leaders, and it has caused two years of highly public civil war with Labour members of Parliament. It helped drive four former Cabinet ministers out of the party altogether to set up the new Social Democratic Party.

In such ways, disciplined, young, militant activists have done much to blacken the party's image in the electorate's eyes.

Though he insists he is not a member, Tony Benn, a former Cabinet minister, has supported them on a number of issues and opposes any expulsion of members or leaders.

The party leadership has now, at last, asserted itself. An official party investigation found what many had known all along. The group violates Labour's constitution by having its own separate committee and financial setup within the party. The annual Labour conference just held in Blackpool ordered expulsion of the Militant leadership.

''But we're not going to go quietly,'' vowed Mr. Taafe to an emotional throng after a recent television interview in an ornate Blackpool hall. ''We might sit down and talk, but we will fight this witchhunt.''

''If the party leaders think they can reverse the radical swing of the grass roots, they are in cloud cuckoo land,'' Mr. Mulhearn told the Monitor between sessions of the Labour conference. ''Poor people are angry at no jobs, no prospects. . . .''

A veteran political reporter for a non-Conservative national daily in London later scoffed at the Tendency's claim to speak for the unemployed. ''Even the recession has produced no real Trotskyite surge of any size,'' he said.

In Mr. Mulhearn's view, however, the Labour party has swung to the right at its top but is moving left at its grass roots.

Bleak, jobless industrial areas like Mr. Mulhearn's Toxteth in Liverpool and Mr. Nellish's Coventry contain many thousands of young people out of work since they left school. They are impatient with Parliament. They are passionately antigovernment.

Ahead now lies months of infighting, potentially damaging to Mr. Foot even though he believes he holds the upper hand today. When Mr. Foot repeated Oct. 3 that he intended to go ahead with expulsions of some kind, Mr. Taafe responded tartly, threatening that the party rank and file would be up in arms if he did.

Both Mr. Mulhearne, Mr. Nellish, and seven other militant members have been endorsed by the party as prospective Labour candidates at the next election.

To expel them now would cause a tremendous row. The nine are likely to be asked to sign a document denying Tendency membership. Several have already denied links to Militant Tendency.

If Mr. Foot can exercise leadership by expelling Militant Tendency leaders, and if the economy stays in recession, his chances of becoming prime minister at the next elections will be greatly improved.

For the United States, that would mean (as Mr. Foot reaffirmed Oct. 3), a British prime minister working to make Britain a nonnuclear state within five years. Mr. Foot also expects to launch a gradual withdrawal of Britain from the Common Market.

If Mr. Foot is unable to squelch the Militant Tendency, however, his image will darken again, together with his hopes for electoral triumph.