Boris Yeltsin and former Soviet Premier Nikolai Ryzhkov registered Saturday as candidates for Russia's first popularly elected presidency, and both chose war heroes as their running mates.

Opinion polls showed Yeltsin, already Russia Federation leader as chairman of its Supreme Soviet, or standing parliament, far ahead of Ryzhkov and other contenders in his quest to gain a popular mandate in the unprecedented June 12 elections in the dominant republic.An explosion ripped through the Democratic Russia center serving as Yeltsin's campaign headquarters late Thursday in the first violence of the election campaign. No one was hurt in the blast.

At least 15 people had announced their intentions to seek the post, which Russian voters created in a March 17 referendum, but only Yeltsin, Ryzhkov, former Interior Minister Vadim Bakatin and several minor candidates filed necessary documents by Saturday, the last day for registration.

Ryzhkov, who suffered a heart attack in December and was replaced the next month as Soviet prime minister by President Mikhail Gorbachev, submitted 1.9 million signatures in support of his candidacy for the Russian presidency, nearly 20 times the required minimum of 100,000.

Yeltsin turned in 300,000 signatures, all gathered in Moscow, where he launched his national political career as the populist head of the Soviet capital's Communist Party from 1985 until Gorbachev fired him in October 1987.

Bakatin, the liberal former interior minister removed by Gorbachev five months ago, submitted 152,000 signatures in support of his long-shot quest to capture the top post in the Russian republic, which takes up three-quarters of the Soviet Union and is home to half its 290 million people.

In a poll released Friday by the National Public Opinion Studies Center, 52 percent of those surveyed said they support Yeltsin, 10 percent backed Ryzhkov and 2 percent chose Bakatin.

Ryzhkov insisted, however, that Yeltin's victory in the voting next month was not a foregone conclusion and that the 61-year-old former premier can mount a strong challenge.

"My credo is, to the maximum degree possible, to defend the people in conditions of reform that are unavoidable," Ryzhkov told reporters Saturday.