Although most informed sources here have been talking for three weeks about the collapse of President Reagan's policies and the confusion within his Cabinet, isolated elements of resistance continue to hold out against a consensus prophesying doom. One of the most original counter-arguments was advanced on Wednesday by M. Duroy, a traveler from Paris who makes periodic visits to the United States to buy real estate and listen to what he calls "the ticking of the bomb."

He arrived in New York in time to read the confessions of David A. Stockman and to follow reports of the quarrel between Alexander Haig, the secretary of state, and Richard Allen, the national security adviser. The behavior of Cabinet officials failed to disturb Duroy. Their cldmsiness he attributed to their self-absorption and lack of political experience. What impressed him was President Reagan's indifference to the fate of his subordinates. Such egoism and coldness of mind, he said, was almost worthy of comparison with the Olympian detachment of the late Charles de Gaulte. Duroy interpreted President Reagan's calm and inattentive smiling as a sign of hope.

"Can you imagine Nixon in the same circumstances," he said, "or Carter? Their weeping piety would have been terrible to behold."

Ordinarily Duroy doesn't trust Americans. A sentimental people, he says, very generous and very intelligent, but too religious. He thinks it a great joke that Americans should have been assigned the character of materialists. A less materialistic society he has yet to encounter. ("Otherwise why would an American care so much for abstractions and so little for architecture, women and cities?") And long ago Duroy came to the unhappy conclusion that the United States is a nation of preachers.

He still regards the Watergauge affair as an absurdity. He remarks that only a people enthralled by the dream of suburban paradise could have made so much of so trifling a crime. Stockman's confessions remind him of Russeau, and as an admirer of Diderot and Voltaire, Duroy associates Rousseau with attrocities committed in the name of high conscience.

I mention these points in order that the reader might appreciate the full extent of Duroy's corrupt and godless cynicism. He is not a man to mourn the death of an illusion, a newt or an ideology.

It was no good trying to impress upon him the monstrousness of Stockman's blasphemy. Borrowing freely from editorials in The New York Times and The Wall Street Journal, I damned Stockman for a treasonable derk. Duroy merely shrugged.

"It is the business of government," he said, "to eat its own words. The man who picks up the first fork is usually made to regret it, but it is better that the thing is done sooner rather than later."

Richard Allen's deep respect for money Duroy both understood and approved, but he wondered why Allen would quarrel with the secretary of state about something so immaterial as the formulation of foreign policy.

As for Haig's furious ambition, Duroy doubted that it ever could be satisfied. Give him a sword, a cocked hat and a map of the world island; leave the rest to heaven or United Technologies.

In Washington, Duroy said, the supply of achievement is very limited and the time in office very short. If a man would make his name, he must forge himself into a legend, a mask, a fable. A huge and busy democracy hasn't got the time to think about the realities of government; it translates its overlords into humors as simple as those presented on a medieval stage. In the persona of innocence portrayed, Stockman could run for governor of Michigan. As the personification of avarice, Allen undoubtedly could make a fortune as a consultant.

"If this is so," said Duroy, "observe the part your president plays."

Because Reagan had already made his name, he said, because he had lived so long in the limelight and seen his face on a thousand magazine covers, he could afford to rest content within himself. Here was his troupe of strolling Cabinet officials, making nonsense of the plot, getting their lines wrong, banging into one another like vaudeville clewns, and yet Reagan didn't feel it necessary to make an entrance on the stage. He had become the head of the studio and, as Sam Goldwyn and Charles de Gaulle had known before him, he would wait for the box office to tell him what to do next.

It comforted Duroy to think that at long last the Americans had elected a president with the fortitude to ignore his critics. "An admirable trait," he said, "in a general or an actor."