Blast Wrecks Office of Yeltsin Supporters : Soviet Union: The suspected bombing is called political terrorism. Some fear that there’s more to come.

MOSCOW — An explosion wrecked the headquarters of the Soviet Union’s biggest anti-Communist coalition, and leaders of the movement on Friday declared themselves the victims of an act of terrorism they said could unleash a chain of political violence in Russia.

“It seems that the biggest act of political terrorism in Moscow in many decades occurred last night,” said Vladimir Boxer, one of the organizers of the Democratic Russia movement, which claims hundreds of thousands of supporters.

“This explosion is a striking, extraordinarily troubling event,” added Gleb Yakunin, a Russian Orthodox priest known for his radical political views. “We’re afraid that this explosion in Moscow is the beginning of a whole series of terrorist acts.”

The apparent bombing may bode ill for the Russian presidential campaign now getting under way between Russian leader Boris N. Yeltsin, who is backed by Democratic Russia, and a group of opponents led by former Prime Minister Nikolai I. Ryzhkov.

The explosion occurred at 10:23 p.m. Thursday, blowing out the front door and knocking down a 15-foot stretch of the one-story building’s wood-and-brick facade, along with much of the roof and inside walls. The single worker still in the building at that hour was only slightly injured. The blast left the centuries-old house--which survived the burning of Moscow by Napoleon in 1812--apparently beyond repair.

Leonid Bogdanov, Democratic Russia’s financial director, said that whoever set the charge had apparently been hoping to destroy lists of tens of thousands of signatures needed to nominate Yeltsin as Russian president and incumbent Gavriil Popov to the revamped post of mayor of Moscow.

Fortunately, Bogdanov said, he had turned in most of the signature lists at the Moscow city council two hours earlier. In any case, he said, Yeltsin and Popov both have gathered more than enough signatures to run in the June 12 elections.

Boxer and other Democratic Russia leaders refrained from accusing any specific group of carrying out the bombing, saying only that “extreme rightist circles” and “fascists” were probably involved.

“It’s hard to say who we suspect,” Bogdanov said. “So far, the KGB is acting normally, but it’s a big agency, and it could be one department doesn’t know what the other is doing. As for our enemies, we have plenty of opponents who don’t approve of Democratic Russia.”

Activists and passersby, peering over police barricades on quiet Staromonetny Alley at the shattered glass and tumbled piles of bricks outside the headquarters, accused Ryzhkov and Communist Party conservatives of engineering the blast, although they admitted that they lacked proof.

“We should have expected such vile things,” retiree and Democratic Russia activist Luisa Dosayeva said. “But they should know that after this, even more people will vote for Yeltsin.”

Experts estimated that up to 11 pounds of explosives would have been needed to produce so powerful an explosion, and Bogdanov said that KGB investigators working through the night had found what appeared to be part of a timing mechanism.

Democratic Russia activists said the KGB investigators had not yet let them into the building to determine the extent of their losses, but they feared that 15,000 campaign posters of Yeltsin had been destroyed, as well as pins and address lists of the movement’s local units.

“A certain disorganization has been introduced at a key moment of the campaign,” Bogdanov said.

The formal nomination period ends Monday, and the campaign is expected to be in full swing next week after it becomes clear who the official candidates are.

Vera Krieger, a Democratic Russia organizer, maintained that the explosion would have no effect on the campaign other than to bring psychological pressure on activists.

She dismissed suggestions that Democratic Russia could have planted the bomb itself to attract more support for Yeltsin, who owes much of his popularity to his image as a martyr persecuted by the Communist Party apparatus.

“We have enough publicity as it is,” she said.

Boxer, too, argued that Yeltsin has so heavily outpolled his competitors in popularity--with a 52% approval rating in a recent survey--that all he wanted was for the race to go smoothly.

Lev Ponomarev, a Yeltsin aide, said he had been particularly disturbed by the murderous intent behind the bomb.

“This didn’t look like a warning bomb,” he said. “It’s evident that the people behind it were prepared for it to bring victims.”

Mysterious bombs have gone off in various military and government establishments in the Baltic republics over recent months, but they have been set to blow at times when no one would be injured.

Normally, at 10:30, there would have been several visitors to the Democratic Russia headquarters, officials said.