Michael Foot's hold on Labour Party weakens as clash with radical opponent Benn intensifies

Is Britain's Labour Party smashing itself to pieces? And has the struggle between party moderates and radical left-wingers become so violent that nobody can halt it?

These questions are being asked openly both inside and outside the Labour movement following a remarkable clash between the party leader, Michael Foot, and the so-called darling of the left, Tony Benn.

The confrontation, which ended with Mr. Foot's public condemnation of Mr. Benn for his failure to accept policies agreed by the ''shadow cabinet'', has led to deep heart searchings within the Labour camp.

It has also, at least for the moment, helped to bring the political futures of both men into doubt, with Mr. Benn increasingly isolated at Westminster and Mr. Foot having to face sharp criticism from senior followers for alleged failures of leadership.

Meanwhile, influenced by the mounting disunity in Labour ranks, the general public seems to be continuing to favor the new Social Democrat-Liberal Party alliance over both Labour and the Conservatives.

The Labour crisis moved into a new phase when Mr. Foot tried to persuade Mr. Benn to move towards the center of the party, by asking him to wind up a parliamentary debate on energy.

But when Mr. Benn delivered his speech he staggered his colleagues by announcing that if and when the Labour Party returned to office it would nationalize North Sea oil companies without compensation.

Labour's energy spokesman, Merlyn Rees immediately threatened to resign. This made it necessary for Mr. Foot to ask Mr. Benn to stick to shadow cabinet policy in the future.

Mr. Benn refused. Soon thereafter Mr. Foot launched a public attack on Mr. Benn in response to pressure from other Labour Members of Parliament (MPs).

The aftermath of the confrontation has made some of Mr. Benn's supporters rethink their commitment. Several members of Labour's left-wing Tribune group told him that they would not be prepared to back him in elections to the shadow cabinet.

This represents only a partial setback for Mr. Benn. His real strength lies in the constituency rank and file, where support for him was 80 percent in elections for the party's deputy leadership which he narrowly lost in September.

But Mr. Foot's position, far from looking stronger after his quarrel with Mr. Benn, looks weaker.

A public opinion poll issued in the week after the clash showed Mr. Foot's popularity to be lower than any party leader since the war. Only 16 percent of voters sampled think he is doing a good job.

These results reached Mr. Foot's desk at the House of Commons as he was preparing a speech to Labour MPs inwhich he charged that the Labour Party had wasted a year arguing with itself about policy and about its leadership.

This anguished admission promises to do Mr. Foot and the Labour Party little good. Under normal conditions, the party should be reaping the benefit of the Thatcher government's failure to come to grips with the economy.

Labour party activists, however, seem to be paying little interest to this and are interested instead in doing battle with each other in matters of party ideology.

Mr. Foot is under pressure to demand the expulsion from the Labour Party of members of the far left. Mr. Foot however has told a party gathering that he was opposed to expulsions.

This had the unintended effect of arousing more dissatisfaction among the moderates who say that their leader has been irresolute and lacking nerve.

But Mr. Foot's dwindling body of supporters claims he has little alternative but to attempt to be a moderating force. Mr. Benn's acknowledged strength among the constituency rank and file means that Mr. Foot would lose, not gain, popularity by pressing any harder.

Mr. Benn has made a few statements trying to mend his fences with alienated supporters, but beyond that he remains unmoved by Mr. Foot's pleas for unity.