Regis Debray, former Marxist revolutionary and apostle of Che Guevara, paid a call on the Reagan White House last weekend--demonstrating that diplomacy, too, makes strange bedfellows.

In an unannounced visit that French officials will not discuss, Debray, who entered the Bolivian jungle to find Guevara and was sentenced to 30 years in prison by Bolivian authorities after they arrested him and killed Guevara, stopped by the White House office of national security adviser Richard V. Allen Saturday.

"Debray, hmm, did I see Regis Debray?" Allen joked when asked about the visit.

"I don't think we can say anything about Regis Debray," a French Embassy spokesman said of the philosopher who is now a foreign policy adviser to French President Francois Mitterrand.

"Is his visit to Washington a secret?" the spokesman was asked.

Long pause, then: "Not exactly a secret, but it was a private, very private and short visit."

The only thing the French Embassy is happy to say about Debray is that he has gone. "The past of Regis Debray is very symbolic. One could think that Debray is a terrorist if one is on the other side," the spokesman said.

President Reagan and Richard Allen have been on the other side all their lives.

"Some people would find it strange that a Dick Allen and a Regis Debray are meeting," Allen remarked as he greeted the French writer and philosopher. "I've followed Regis Debray for 15 years. Nothing he could say would surprise me. We know quite a bit about each other," Allen said of the former advocate of violent revolution. Debray has abandoned his militant Marxist positions in favor of membership in the French Socialist Party.

Allen said that Debray requested the meeting and that it was very cursory. In an exchange for which the diplomatic phrase "agree to disagree" would certainly be a gentle understatement, Allen told Debray what Reagan's positions are and Debray stated some of his positions.

The presence of Debray as an adviser to Mitterrand concentrating on Latin American affairs has long annoyed some U.S. officials.

In 1967, when Debray entered Bolivia, he had written a book called "Revolution in the Revolution," setting forth a doctrine for revolution in Latin America that rejected both the Soviet and Chinese revolutions as models. Guevara had dropped from sight in 1965 amid much speculation, and Debray drew world attention with this statement in the book:

"When Che Guevara reappears, it is hardly risky to assert that it will be as the head of a guerrilla movement, as its unquestioned political and military leader." Within the year Guevara was dead.

But 1967 is a long time ago and Debray, in addition to joining the Socialists, has repudiated some of his early work. Now 40, Debray, who served only three years of his Bolivian prison term before being released after appeals from French and other intellectuals, told an interviewer in 1970 that much of what he wrote in "Revolution in the Revolution" "seems to me today to be so weak, so arguable."