A Middle East terrorist group said today it was responsible for planting a bomb in a French high-speed train yesterday and reiterated earlier demands for the release of Arab political prisoners held in France.

The group, which has already asserted responsibility for bomb attacks against civilian targets in Paris in recent months, said it was prepared to launch a "new series" of attacks unless the prisoners were released. Ten persons were slightly injured in the latest explosion, which occurred in the baggage area of a passenger car on a train bound from Paris to the southeastern city of Lyons.

The demands for the release of Arab prisoners in French jails follow similar calls by pro-Iranian groups in Lebanon, who have seized eight Frenchmen over the past year. The Islamic extremists have said they have already killed one of their hostages and will kill others unless the French government fulfills their demands.

The outgoing Socialist administration headed by Prime Minister Laurent Fabius refused to give in to what it described as "blackmail," a stand supported by the new right-wing majority in the National Assembly. The government has, however, sent a number of emissaries to the Middle East to try to make contact with the kidnapers.

There has been little diplomatic activity in the hostage crisis since Sunday's election. An unofficial emissary, Dr. Razah Raad, who was sent by the French government to Lebanon last week, announced today that he was giving up his efforts to secure the release of the hostages following criticism of his role in the press.

A Lebanese-born physician, Raad said that he made contact with representatives of the kidnapers last week and was in a position to negotiate a deal with the French government. This was subsequently denied by Islamic Jihad, which claims to be holding three of the hostages.

Islamic Jihad has called for the release of a five-man commando team convicted of the attempted assassination of former Iranian prime minister Shahpour Bakhtiar in Paris in July 1980. Freedom for the leader of the team, Anis Naccache, is also one of the demands of the group that has claimed responsibility for the bombings in France.