Speaking to thousands of supporters gathered in the stadium used for the 1980 Moscow Olympics opening and closing ceremonies, Vladimir Putin, who tops the party's election list, said: "In order for the future parliament and president to work efficiently, cooperating with each other for the benefit of people, we need victory."
Putin said it was vital to ensure the continuity of current policy through the parliamentary and presidential polls in December and March respectively.
"The current stability, economic growth, peace, and rising, albeit moderately, living standards are the result of the continuous political struggle at home and on the world scene," Putin said, warning that the West would prefer to see "a weak, ill Russia with a disorganized and split society."
He also said some political forces inside the country were seeking support from foreign governments and funds, rather than their own people. Criticizing Western-leaning opposition groups, he said they were attempting to restore an "oligarchic regime based on corruption and lies," referring to the turbulent 1990s which brought fortunes to a handful of Kremlin-connected tycoons while impoverishing millions of ordinary Russians.
"They are planning to take to the streets. They have been trained by Western experts, have gained some experience in neighboring [ex-Soviet] republics, and will now try their hand here," the president said, without specifying names or organizations.
While Putin heads the United Party candidate list, he is not a party member and may choose not to take a seat in the State Duma, the lower house of parliament. He has so far declined supporters' appeals to amend the Constitution and run for a third consecutive term, at the same time refusing to be drawn on his future plans.
Putin's move to head United Russia's candidate list has been seen as designed to secure a large parliamentary majority for the party and help the Kremlin further tighten its grip on the political system.
The latest opinion surveys put United Russia in the lead with a little under 60% of popular support, slightly down on previous weeks. The Communists and the nationalist Liberal Democrats are the only two other forces likely to overcome the 7% threshold for the State Duma.
Other parties, including the liberal Yabloko and Union of Right Forces - champions of western-style democracy and free market reforms in the 1990s - are likely to receive 1% of the vote in December's polls.
A number of opposition parties in the coalition The Other Russia movement, including chess grandmaster Garry Kasparov's United Civic Front, have been denied registration for the upcoming elections.