Prime Minister Margaret Thatcher urged other European allies today to join Britain in backing with action as well as word the U.S. response to the Soviet invasion of Afghanistan.

She said they must put aside their "differences of emphasis" and unite behind President Carter's "clear leadership." Efforts by the West to defend itself against the Soviet threat, Thatcher said, "can only be effective if we are united."

Her speech, opening a major parliamentary debate on the Afghan crisis, comes a week before East-West relations are to be taken up by the European Economic Community in Brussels.

The nine-member EEC is to consider calls by Carter and Thatcher to move or boycott the Summer Olympics in Moscow and efforts by Britain to cut off the subsidized sale of surplus Common Market butter, poultry and sugar to the Soviet Union. While Britain has championed such retaliatory moves by the Common Market, France has led opposition to them.

In a pointed reference to France today, Thatcher recalled the "superb response" of president Charles de Gaulle to an emissary of president Kennedy during the 1962 Cuba missile crisis. Quoting de Gaulle as saying, "You may tell the president that France will support him," Thatcher declared that "Europe should send the same message today."

But today's parliamentary debate also brought out into the open "differences of emphasis" within Britain's own political leadership over its self-appointed role as the European broker for Carter's get-tough policy.

Former prime minister James Callaghan, now leader of the Labor Party opposition, condemned the Soviets for invading Afghanistan and said, "We must strongly support the Carter doctrine" of threatening military resistance to Soviet moves in the Persian Gulf area.

But Callaghan went on to criticize Thatcher, without naming her, for what one influential political columnist here has callec "britain's almost poodle-like support for the United States." Calllaghan said Britain should join France and West Germany in continuing "to seek out areas for negotiation and conciliation with the Soviet Union."

Former prime minister Edward Heath, Thatcher's predecessor as Conservative Party leader, said that in improving relations with some countries of the Third World, the West "is going to have to forego some things we've insisted on, like human rights." He criticized both the United States and Europe for having "left in a large part of the world a great credibility gap" by "doing nothing" in the past several years while the Soviets interfered in formerly nonaligned countries.

Joining Thatcher in urging "a united European approach," Heath said Britain "should not let the Soviet Union separate the United States from its European allies."

British leaders are divided over what to do about the Summer Olympics. Heath, who pointed out that he has captained two British yachting teams in international competition, opposed moving or boycotting the Olympics.

Thatcher reiterated that the Moscow games were a "political" event and attending them would "give aid and encouragement" to the Soviets. But she added that if their campaign to move them fails, she could only "consider further what advice, and it could only be advice, we should give" to the British Olympic Committee.