The move to unite the left-leaning Party of Life and Rodina (Motherland) with the Party of Pensioners was announced in late August.
"The deadline for creating the party is the start of December," Igor Zotov said. "So a founding congress should be held before November 1."
Sergei Mironov, who leads the Party of Life and is speaker of the Federation Council, said the new three-party alliance would have about 500,000 members, which would bring it close to Russia's traditional left-wing party, the Communist Party, and its 580,000 members.
Neither the Party of Life nor the Pensioners won enough votes in the 2003 election to take up seats in the lower house of parliament, the State Duma. The Communists won 12.6% of the vote.
Although Rodina, running as an electoral bloc with a campaign focusing on the disparity between many ordinary people and tycoons, stormed into the Duma at the first attempt with just over 9% of the vote, it has since been beset by problems. Leaders have come and gone, and it courted controversy with a television advertisement in the campaign for the Moscow legislature this year that was called overtly racist by many and was eventually banned.
However, all three leaders dismissed the suggestion that the new party was a Kremlin project. Media speculated over the summer a new, controllable left-wing party could be established at the behest of the Kremlin authorities.
The Federation Council speaker said the new party would take up opposition to United Russia, the current "party of power," which holds a massive majority in the Duma.
"We oppose the very essence of United Russia as the monopoly political force of the party of power," said Mironov, who is thought to be close to President Vladimir Putin.
"We are in favor of a genuine multi-party system in Russia and, therefore, are in opposition to United Russia," he said.
The leaders said the party would run in the 2007 Duma election and would consider who would run as a candidate in the 2008 presidential election. Mironov finished last in the 2004 presidential contest with only 0.8% of the vote and a then Rodina leader, economist Sergei Glazyev, came in third with just over 4%. Putin won by a landslide with 71%.
Mironov said it was too early to talk about a candidate and he added that the party could accept other forces.
