President Reagan, with the backing of the French, intends to urge British Prime Minister Margaret Thatcher to stop one step short of total military victory in the Falklands war and allow time for a negotiated settlement, administration officials said today.

"We'd like to see a display of Churchillian magnanimity," said a well-placed White House official in advance of Friday's private meeting between Reagan and Thatcher.

The thrust of Reagan's attempted friendly persuasion of Thatcher is described as an effort to convince her it is prudent for the British to delay their scheduled assault on Stanley for several days to allow a final attempt at a negotiated settlement.

Britain maintained a blackout of news on any fighting in the Falkland. Details on Page A22.

Officially, both U.S. and French officials were reluctant to comment publicly today on any efforts to persuade Thatcher to modify her position. Both governments are concerned, as one U.S. official said, that "it would be counterproductive if it appeared that anyone was trying to strong-arm the British into doing something they don't want to do."

But the Falklands conflict was a principal item of discussion today at a meeting between Reagan and French President Francois Mitterrand that Secretary of State Alexander M. Haig Jr. described as "frank and intimate."

After the meeting, Haig told reporters gathered for the eighth economic summit meeting which formally opens Friday night in Versailles that Reagan and Mitterrand had no differences on the Falklands issue.

"With respect to the Falklands, both leaders are concerned that the conflict terminate at the earliest possible date," Haig said, reiterating that this termination should be based on United Nations Resolution 502, which calls for withdrawal of Argentine forces.

So far, there is no sign that a U.S. entreaty on the Falklands will prove successful. Administration officials acknowledged that there was no demonstrable impact from a telephone call by Reagan to Thatcher on the same theme earlier this week, although they denied a televised report that the British prime minister had been angered by Reagan's phone call.

But Friday's meeting, Haig said, will allow Reagan and Thatcher to "plumb in depth" each other's feelings about the war.

Reagan, who has made no secret of his own sympathy for the British, is said to have become convinced in recent days that the long-range negative consequences of the war on U.S. relations with South American nations make a last try at negotiations worthwhile.

Thatcher's own comments have not offered much encouragement to either the French or U.S. governments. In an interview with The Washington Post yesterday, the prime minister said Argentina had only a few days to withdraw its troops before the battle for the Falklands capital, Stanley.

In television interviews with British networks the same day, Thatcher responded sharply to the suggestion that she show "magnanimity" in victory. "It is not a word I use in connection with the battle for the Falklands," she said. "Sometimes I think people are using it to say, 'All right, hand something to the Argentines,'"

Because of Thatcher's militance, neither the U.S. nor the French side is especially optimistic that she will delay the start of the attack on Stanley. A highranking French official, more openly pessimistic than any American, said: "It's been several days since we've heard the word 'negotiations' coming out of a British mouth."