Belgian police have arrested four suspects in a 14-month bombing campaign by a mysterious left-wing group, the Justice Ministry said tonight.

The arrests appeared to be the first breakthrough for investigators since the attacks claimed by the group, the Fighting Communist Cells, began in October 1984. Twenty-eight targets -- North Atlantic Treaty Organization facilities, U.S. defense contractors and Belgian business and government offices -- have been hit and two persons killed in the bombings.

The Belgian police force had come under increasing criticism recently for its inability to stop the bombings and other violence.

The suspects, three men and a woman, were arrested in the midafternoon by about 30 undercover agents who surrounded them in a fast-food restaurant in the southern city of Namur, police officials said. The suspects were heavily armed but offered no resistance.

Police said they were searching for a fifth suspect seen leaving the restaurant shortly before the arrests.

One of the four was identified by the Justice Ministry as Pierre Carette, 33, a Belgian and a former printer who is believed by investigators to be one of the leaders of the group, known as the CCC after its French name.

Carette also has been linked by police to the French terrorist group Direct Action, as well as to an unsuccessful 1979 bombing in Belgium that narrowly missed the car carrying Gen. Alexander Haig Jr., then the NATO commander.

Some police investigators reportedly believe there is firm evidence that the CCC, Direct Action and the West German Red Army Faction have cooperated in producing the wave of terrorism in Belgium, France and West Germany in the past year.

The CCC, however, has carried out its own distinctive campaign, avoiding the assassinations and bombings designed to kill civilians that have been seen in France and West Germany.

While the group's tactics and Marxist rhetoric have embarrassed Belgian leftists, stopping its well-planned attacks has become a major preoccupation for the center-right government of Prime Minister Wilfried Martens. This month, the government rejected demands by opposition Socialist parties for a parliamentary inquiry into the bombings and other violence, which have shattered Belgium's traditional image as one of the most tranquil nations in Western Europe.

Justice Minister Jean Gol said that the commission would interfere with police work, but Socialist officials charged that the government feared revelations about the lack of police readiness.

One national magazine said recently, "Our police force is sick, very sick. . . . Belgium, which has the highest percentage of police in the European Community, is today a kind of laboratory of failure in crime-stopping."

Another magazine ridiculed Gol and Interior Minister Charles-Ferdinand Nothomb, portraying them on its cover as cartoon characters floating on a cloud under a title that read, "The Impotent Ones."

Police and government officials admit that despite serious outbreaks of terrorism in neighboring countries such as West Germany and Italy in the 1970s, Belgium failed to prepare its security forces to fight that kind of threat.

"Belgians could never believe something like this could happen here," said Christian Lepage, a Brussels police commissioner.

At first, the CCC was cautious, placing bombs in the middle of the night. But in recent weeks, its members have become increasingly bold, walking into downtown banks and offices during working hours and leaving time bombs, along with leaflets warning of the explosions.

Police managed to clear those offices before the explosions, but two firemen were killed last May as they approached a CCC car bomb in downtown Brussels.

Faced with almost weekly bombings this fall, the government mobilized six companies of paratroops to assist local and national police.

But criminology and terrorism experts here say that fundamental changes need to be made in the police force if it is to deal effectively with political violence and steadily increasing domestic crime.

Lepage, who studied at the FBI Academy, places part of the blame for police deficiencies on inadequate training and funds.

Belgium's security forces were widely criticized for failing to halt the violence that killed 39 persons at the European Cup soccer championship in Brussels in May and a parliamentary inquiry criticized the Interior Ministry's security preparations for the match.

This fall, the country has been shocked by the reappearance of a gang of gunmen who methodically hold up supermarkets and shoot down bystanders.

Seventeen persons, including several children, have been killed in three attacks by the gang, which remains at large.