Bombs exploded in two large department stores packed with Christmas shoppers here today, injuring 25 persons in the latest of a series of terrorist incidents across Western Europe.

Police said that the two bombs, which went off within minutes of each other during the heaviest shopping period, appeared timed to cause maximum panic at the start of the holiday season. But the amount of explosive used was relatively small.

Several telephone calls from persons claiming responsibility for the blasts were received by news organizations in Paris, including one from someone claiming to be speaking for the Palestine Liberation Front, but police were skeptical about their authenticity.

The latest explosions in Paris follow a string of attacks against targets identified with the North Atlantic Treaty Organization in France, Belgium and West Germany. One person was killed Friday when a bomb, apparently intended for Belgium's justice minister, exploded in a crowded courthouse in the eastern Belgian city of Liege.

A Belgian terrorist group calling itself the Fighting Communist Cells claimed responsibility for other bomb attacks Friday against a NATO office in Versailles, outside Paris, and a NATO pipeline outside Paris. Investigators believe that the Belgian group is linked to a French group known as Direct Action and the West German Red Army Faction.

It is unclear whether these left-wing terrorist groups also could be involved in a separate series of attacks on department stores in Paris. The last such attack was in February, when one person was killed as a bomb exploded outside the British-owned store of Marks and Spencer.

The spate of bombings is a worrying phenomenon for West European governments, which thought they had largely defeated urban terrorism as a political force. As the numbers of terrorists have declined, their tactics appear to have changed: Instead of seeking popular support, they now concentrate on forming small, tightknit groups that operate across Europe's loosely controlled frontiers.

The first bomb this afternoon went off shortly after 5:30 p.m. in the china department in the basement of Galeries Lafayette, on the Boulevard Haussman in the heart of the capital's commercial district. Twenty persons were injured, six seriously.

As panic spread throughout the store, and crowds emptied into the street outside, there was a second explosion 100 yards down the same street at the Printemps store. The target this time was the perfume department on the ground floor. Five persons were injured, including two seriously.

Eyewitnesses said that shortly after the explosions they saw two men running toward a white Renault car. An investigation of the license plate number indicated that the car had been stolen.

Rescue work was hampered by rush-hour traffic, which had been building up in the center of Paris. For several hours afterward, sounds of sirens filled the streets as police vehicles and fire engines tried to make their way through the traffic and crowds.

Security was tightened at public buildings throughout the city, including the National Assembly and foreign embassies. A thorough search also was conducted at the Parc de Princes stadium after the anonymous caller claiming to speak for the Palestine Liberation Front said that a third bomb would go off at a soccer game.

Today's bombings produced immediate calls for tougher action against terrorists from the right-wing opposition, including some demands for the reinstitution of the death penalty, which was abolished by the Socialist government soon after it came to power in May 1981.

"Society is at war against terrorism. It must be able to defend itself. Not with words, but with acts," said the deputy mayor of Paris, Jean-Pierre Pierre-Bloch.

The Paris office of the Palestine Liberation Organization issued a statement condemning the bombings as "criminal" and denying PLO involvement.