A series of explosions damaged NATO's emergency fuel pipeline at several points in southern Belgium today. The same mysterious leftist group that carried out several other bombings in the country this fall claimed responsibility for the blasts.

The latest bombings, which came two days before foreign ministers of the North Atlantic Treaty Organization are to begin their biannual meeting here, caused no injuries but seriously damaged valves, opened fuel lines and started fires in two places, a NATO spokesman and Belgian officials said.

The NATO spokesman said the six predawn blasts forced the shutdown of a major pipeline carrying fuel from Antwerp to military air bases in West Germany for about 48 hours while repairs were made. In the meantime, the air bases will use fuel supplies in storage or sent through other NATO pipelines that run from the Belgian coast through northern France, the spokesman said.

The damaged sections are part of a 3,680-mile pipeline that runs through Belgium, France, West Germany, the Netherlands and Luxembourg. Part of the system is used in peacetime by civilian companies to transport fuel, but in the event of a military crisis, a U.S. official at NATO headquarters said, the entire pipeline would be taken over and used to supply fuel to allied forces.

The bombings were claimed by the Communist Combatant Cells, the group that has taken responsibility for six other attacks in Belgium since the beginning of October. In a four-page letter delivered to a Brussels newspaper, the group said the bombings were part of a "war against NATO" and "military imperialism" that also was being fought by "Communist Combatants" in other NATO nations.

The group has eluded attempts by Belgian authorities to track down its members or even identify its origins.

In mid-October, after bombings against offices of Prime Minister Wilfried Martens and the American defense contractor Honeywell Inc., Belgian police carried out surprise searches of more than 100 homes and offices.

The police seized documents and brought in 15 people for questioning, all of whom were released the same day. The raid provoked a political controversy because the government only ordered searches of the offices of leftist groups and their members.

Belgian leftist groups have joined with mainstream political parties in condemning the bombings.

In its communiques, the group has denied speculation in the Belgian press that it is connected to the French terrorist group Direct Action. The NATO spokesman said the French usage in the group's letters indicated that the writer was Belgian. "They are amateurs, but skillful," the spokesman said.

The group has so far avoided bombing targets where there could be a loss of life, but a U.S. official at NATO headquarters said the latest attacks made "everybody extra edgy," given the arrival of Secretary of State George P. Shultz Wednesday for the NATO meeting.

"There is concern that we don't know as much about this group as we'd like to," the U.S. official said. Security was tightened at NATO headquarters in the Brussels suburb of Evere this fall after the earlier bombings.

The group said in a letter sent to news organizations in October that it wished to launch the "armed military political struggle in this country [Belgium], which until now has been too little touched by the struggle for communism."