resident Reagan, in a militant speech to members of the British Parliament, today proposed a "crusade for freedom" that would actively challenge the Soviet Union and assist "democratic development" throughout the world.

Speaking in the Royal Gallery of the House of Lords, where the walls are decorated with paintings of British military victories and statues of long-dead kings, Reagan alternately described the Soviet Union as a military menace and as a faltering repressive system that is decaying from within.

The president called for a response to the Soviet challenge that includes both military preparedness and the export of democratic ideas.

"At the same time we invite the Soviet Union to consider with us how the competition of ideas and values--which it is committed to support--can be conducted on a peaceful and reciprocal basis," the president said. "For example, I am prepared to offer President Brezhnev an opportunity to speak to the American people on our television if he will allow me the same opportunity with the Soviet people."

Reagan's proposal for an exchange of television broadcasts--presumably along the lines of those exchanged by Brezhnev and then-president Nixon in 1972--won applause from the 500 members of the House of Lords and House of Commons.

The only other time the speech was similarly interrupted was when the president, in the strongest language he has so far used on the Falklands conflict, expressed unequivocal support for Britain.

"On distant islands in the South Atlantic, young men are fighting for Britain," Reagan said. "And, yes, voices have been raised protesting their sacrifice for lumps of rock and earth so far away. But these young men aren't fighting for mere real estate, they fight for a cause, for the belief that armed aggression must not be allowed to succeed and that people must participate in the decisions of government under the rule of law."

Before he finished this last sentence the president was stopped by a rising, murmur of approval, punctuated with shouts of "Hear, hear," that welled from his audience and became a cheer. When it had subsided, Reagan completed his sentence and said: "If there had been firmer support for that principle some 45 years ago, perhaps our generation wouldn't have suffered the bloodletting of World War II."

Reagan's reference appeared to touch an emotional wellspring among members of Parliament whose World War II memories already have been roused by the fighting for the Falklands.

The words Reagan used today--including "crusade for freedom," the title of Dwight D. Eisenhower's account of the European phase of World War II--were designed to capture these emotions. But Reagan also sought to couch his anti-Soviet expressions in terms that would not undermine his commitment to peace or to the nuclear arms reduction talks that will begin in Geneva on June 29.

These conflicting aims produced a speech that was ideological in content, moderate in purpose and conflicting in tone. At one point, Reagan spoke of "the march of freedom and democracy which leave Marxism-Leninism on the ash heap of history as it has left other tyrannies which stifle the freedom and muzzle the self-expression of the people." In another passage, he said the difficult goal of the West was to "preserve freedom as well as peace."

Reagan's speech was consistent with the theme of a National Security Council directive he approved last month which called for "shrinkage or disillusion" of the Soviet Union through military preparedness, economic means and a "political-propaganda offensive."

At times Reagan seemed to be debating with himself just how far the United States should go in its campaign to promote democracy in developing countries and those under Soviet sway. He said the West "must be cautious about forcing the pace of change" while always declaring its ultimate commitment to freedom. But he repeatedly called attention to Soviet repression in Poland, Afghanistan and Southeast Asia.

After observing that "freedom is not the sole prerogative of a lucky few but the inalienable and universal right of all human beings," Reagan said: "The objective I propose is quite simple to state: to foster the infrastructure of democracy--the system of a free press, unions, political parties, universities--which allows a people to choose their own way, develop their own culture, to reconcile their own differences through peaceful means."

The president was vague about how he expected to export democratic ideas beyond saying that the chairmen and leaders of the Republican and Democratic parties in the United States were "initiating a study with a bipartisan American political foundation to determine how the United States can best contribute--as a nation--to the global campaign for democracy now gathering force."

It was the first speech ever given by an American president in the richly decorated Royal Gallery, which is part of the Palace of Westminster. British Prime Minister Margaret Thatcher had wanted the president to speak in Westminster Hall, the most historic building in Britain, but a premature announcement of this in the United States by a Reagan aide before Thatcher had time to consult with Labor Party leaders dashed any hope of such an appearance.

Members of Thatcher's Conservative Party predominated in the audience today. Only 30 members of the minority Labor Party showed up, although this contingent included most of the party leadership, including two former prime ministers.

Opponents of the Reagan visit held a day-long teach-in at nearby Westminster Central Hall where the speakers included Dame Judith Hart, chairman of the Labor Party.

In a toast to Reagan at a reception given for him at 10 Downing St., Thatcher called his speech "a triumph" and praised it "for putting freedom on the offensive where it belonged."

Former prime minister Edward Heath, also a Conservative, was more critical. He said that the British "knew about communism" without the need of any instruction from Reagan, and added: "The younger generation isn't going to feel much for democracy when there are 30 million people unemployed in the West."