French and Algerians mystified by Mitterrand's trips to Morocco and Portugal

The mystery remains total - and tantalizing. What was French President Francois Mitterrand trying to accomplish by paying two surprise visits last week to Morocco, meeting King Hassan last Thursday, then leaving Friday for Portugal, only to return to spend Saturday and Sunday in Fes? The Elysee Palace would say only that the visit was ''private'' and ''a vacation.''

No one here believes that. Speculation abounds that talks were held about the recent Moroccan-Libyan unity pact and the standoff in Chad, where Libyan troops face 3,000 French troops. The immediate result of this diplomacy was to spark controversy at home and abroad.

Algeria is furious. Already worried about the pact between Morocco and Libya, it now fears a French tilt toward Morocco that would further isolate it. When Algeria summoned the French charge d'affaires to its Foreign Ministry in Algiers , it found the French explanations unsatisfactory. An Algerian government newspaper has attacked French policy as ''neocolonialist.''

At home, human rights activists are mad. While Mitterrand was in Morocco, 33 men jailed since last January's riots over bread prices continued on a hunger strike. Several are reportedly in serious condition.

''How can Mr. Mitterrand go to Russia and speak on behalf of (Andrei) Sakharov and go to Morocco when these people are dying?'' a television commentator asked.

Mitterrand was also ran into flack over the secrecy surrounding his trip. ''No Frenchmen can believe that Francois Mitterrand can go to Morocco like you and me for a vacation with Club Mediterranee,'' commented the normally pro-government newspaper Le Matin.

At time of writing, no explanations were forthcoming. Suggestions that a breakthrough on Chad was imminent were quieted when Defense Minister Charles Hernu said that French troops ''would stay where they are for now.''