Within an hour of the presentation of the Conservative Party manifesto this morning, Michael Foot, leader of Britain's opposition Labor Party accused Prime Minister Margaret Thatcher on national radio of wreaking more havoc on the country's economy than Adolf Hitler's World War II bombers.

Thatcher herself declared at a press conference that in 33 years of political experience she had never encountered policies of such "extreme socialism" as those being put forward this spring by Labor. She said she had read the party's platform with "mounting horror" and victory by Labor would be a "catastrophe."

"They would change the nature of our society," she warned.

One week into Britain's month-long general election campaign, the rhetorical abuse already exchanged marks this as one of the country's bitterest of modern times. "The choice before the nation is stark," Thatcher said today in releasing her Conservatives' proposed program for a second term, and voters would likely agree.

The Conservatives are outlining a policy of continued tight fiscal restraint, of major new curbs on the power of trade unions, the selling off of more nationalized industries and a commitment to a stronger national defense. The thrust of their platform is combative and confident. "Britain is once more a force to be reckoned with," asserts the Tory manifesto's opening line.

Labor is pledged to a massive input of public money to spur the economy and create jobs; substantial devaluation of the pound; part or full nationalization of such key industries as electronics, pharmaceuticals and building equipment; renunciation of nuclear weapons and withdrawal from the European Community.

This "emergency" program of radical change, Foot contends in his introduction to the Labor platform, offers a "real alternative to the economic and industrial disaster which modern Conservatism has inflicted."

Holding to the center is the Alliance of the Liberals and Social Democrats, running a weak third in the opinion polls. Their program of modest reflation, of reasoned partnership between industry and labor and a defense strategy of limiting nuclear weapons is being overshadowed by the acrimony of the two larger parties.

One important explanation for the campaign's rough-and-tumble character so far is Thatcher's behavior. In public statements, she has been playing to her reputation as the "Iron Lady" to the point of frequently adopting military metaphors. Asked yesterday why she would not go to the meeting of European Community prime ministers long scheduled for two days before the June 9 polling, Thatcher retorted: "A general does not leave the field of battle when coming up to the climax."

Within a few hours, the summit was postponed by its chairman, West German Chancellor Helmut Kohl, until after the election.

At today's press conference, flanked by her key ministers, Thatcher demolished questioners whose point of view she found disagreeable. "You're wrong, wrong, wrong," she replied testily to one question about economic policy. "I trust you've taken that message." When Foreign Secretary Francis Pym appeared in another answer to be less forceful on the future of the Falkland Islands than Thatcher plainly would have liked, she abruptly corrected him.

Later, asked why she had not commented on the Alliance's program, Thatcher said, "I wouldn't put anything second-rate before you."

Labor has responded to the Thatcher challenge by having its spokesmen accuse her of virtually dictatorial control over her party. "It is dangerous to put the destiny of a party or a country in the hands of a single person," Denis Healey, Labor's deputy leader, asserted yesterday, "even one more sensitive and less pig-headed than the prime minister."

But underlying this atmosphere of vituperation are fundamental political differences. As is the case in the United States, the election platforms of British parties are often modified in practice once the balloting is over. This time, the situation is different.

The Labor Party--which in one major poll this week cut the Tory lead in half to only seven percentage points--is committed to more sweeping changes than when it governed Britain during much of the 1960s and 1970s. The leftward swing of the party since the last election in 1979 has been pronounced.

The Conservatives are also more unified. Thatcher has supplanted most of those ministers who favored moderate economic and social policies, and those who remain are not expected to be reappointed.