French police detained 51 suspected Armenian activists today and confiscated weapons and explosives following Friday's terrorist bombing at Orly Airport that killed six people, including one American, and injured 56.

An Interior Ministry spokesman said the Armenians were detained because they could have information about the Armenian Secret Army for the Liberation of Armenia, which has claimed responsibility for Friday's blast and a string of other terrorist acts in Europe and North America.

The Orly bombing has focused attention here on one of the most intractable of Middle East problems. The Secret Army was founded in 1975 to avenge what it describes as the massacre of about 1.5 million Armenians in Turkey during World War I, an event Turkish officials describe as an invention of Armenian propagandists.

During the past eight years, more than 20 Turkish diplomats and members of their families have been killed around the world and 60 others wounded in attacks for which responsibility has been claimed by Armenian terrorists--often the Secret Army's right-wing rival, the Justice Commandos of the Armenian Genocide.

The most recent such attack, the assassination of a Turkish Embassy attache in Brussels last Thursday, was claimed by the Secret Army, the Justice Commandos and a third Armenian terrorist group. But Friday's bombing of the Turkish Airlines counter at Orly suggested that the Secret Army, reacting to the increased protection for Turkish embassies and consulates in Paris and other cities, was turning increasingly to more indiscriminate terrorism.

In the past, the Secret Army has claimed the assassinations of the Turkish ambassadors to Austria, France, the Vatican and Yugoslavia. In France alone, Armenian terrorist groups have carried out at least 14 attacks against Turkish targets during the past three years.

The Orly Airport bombing was promptly condemned by leading Armenian emigre organizations. A spokesman for the right-wing Tashnak Party described the bombing as an "act of blind terrorism" and charged that the Secret Army had become "an instrument of the Soviet Union" from its base in Syria.

The Tashnak spokesman, Henry Papazian, told a press conference here that he had information disproving assertions by the Secret Army that its leader, Hagop Hagopian, was killed during the Israeli bombardment of Beirut in July 1982. Papazian said that Hagopian now uses the name Mihran Mihranian.

The independent leftist newspaper Liberation also reported today that Hagopian was still alive and had visited Paris in April. According to this report, which could not be confirmed independently, French police refrained from arresting Hagopian because officials feared reprisals.

The Tashnak spokesman said that the use of France as a site for terrorist attacks could mean either that negotiations for an accommodation between the French government and the Secret Army had failed or that the terrorists were being used by "other governments" to destabilize France.

The French government, while strongly condemning terrorism, has taken a generally sympathetic view of Armenian grievances. Last week Foreign Minister Claude Cheysson implicitly criticized Turkey for failing to acknowledge the massacres of Armenians in 1915.

The string of terrorist attacks in France has strained relations between Ankara and Paris. Turkish officials have criticized the French government for allowing terrorists to operate on its territory--a charge that has been angrily denied here.

The Armenians were promised an independent homeland by President Woodrow Wilson after World War I when the defeated Ottoman Empire was split up. But the plan was opposed by both the Soviet Union and Turkey, which between them occupied the territory claimed by Armenia. In the Treaty of Lausanne of 1923, which settled Turkey's new borders, there was no mention of an independent Armenia.

Today up to 7 million Armenians, descendants of one of the most ancient Christian nations, are scattered around the world. The largest community, nearly 3 million strong, lives in the Soviet republic of Armenia, with another 1.5 million in other parts of the Soviet Union. More than half a million Armenians live in the United States, about 100,000 of them in California. There are about 300,000 in France and roughly 100,000 in Turkey. The terrorist groups, although some like the Secret Army claim hundreds of members, represent a tiny fraction of the world's Armenian communities.

Among the weapons confiscated by French police today were submachine guns, two pounds of explosives, detonators and automatic pistols. Police said, however, that they still had no evidence linking those detained to the Orly bombing. In France, suspects can be held up to 48 hours for questioning without charges.

On Saturday, in a telephone call to the French news agency in Athens, a man who claimed to be speaking for the Secret Army threatened new terrorist attacks against an unidentified country holding Armenian prisoners. At least eight countries fall into this category, including the United States, Canada and Britain.