The Duma is the only chamber of the national legislature that is directly elected. Since the last election in 2007, the United Russia party headed by Prime Minister Vladimir Putin has held 315 of the 450 seats, while opposition parties were squeezed out.

The three other parties — the Communists, the nationalist Liberal Democratic Party and the populist Just Russia — generally offer little opposition and support the Kremlin in most initiatives.

Another group expected to take part in the December vote is Right Cause, a Kremlin-friendly party headed by Russian tycoon and New Jersey Nets basketball team owner Mikhail Prokhorov.

Right Cause is widely seen as a Kremlin creation designed to lure opposition-minded, pro-business voters, while building an illusion of competition with Putin’s United Russia.

Medvedev made the announcement during a meeting with leaders of political parties with a presence in the Duma at his summer residence in Sochi.

“I would very much want the makeup of our future Duma to maximally reflect the political preferences of the widest range of our citizens,” Medvedev said in televised remarks.

The election is to be followed by the presidential vote in March — with speculation rampant about whether Medvedev will run for a second term or cede his seat to his mentor Vladimir Putin, who won two elections in 2000 and 2008 and was constitutionally barred from running for a third consecutive term.

Under a 2005 election law, all seats in the Duma are chosen by proportional representation, and a party must get at least 7 percent of the national vote to qualify for seats. During the 2007 vote, opposition, human rights and vote-monitoring groups claimed the Kremlin orchestrated widespread machinations aimed at ensuring a high turnout and a big United Russia win.

Medvedev acknowledged the claims in his address.

“Two things are equally unacceptable to us — the administrative lawlessness of officials who are trying to manipulate the elections ... and ungrounded claims of falsifications that we often hear from those who lost,” he said.

Before the 2007 vote, half the Duma’s seats were filled by candidates from individual races, rather than party lists, allowing independents and members of small parties a hypothetical chance.

Only officially registered parties are eligible for votes, and official scrutiny serves as an effective tool to deny registration to Kremlin critics and liberal parties.

One of them was the People’s Freedom Party, known by its Russian acronym as Parnas and founded by three prominent opposition leaders. In June, the Justice Ministry said the party could not be registered because the ministry had found violations in the required 45,000 signatures the party had submitted with its application.

One of the party’s leaders, former Prime Minister Mikhail Kasyanov, said some people who joined had been summoned by police or security officers who asked why they had joined the opposition party and whether they understood they could lose their jobs or their children would lose the opportunity to study at university.

Meanwhile, a handful of leftist and liberal activists rallied in front of the Central Election Commission in central Moscow to protest the Kremlin policies of excluding their parties from political life.

Three of them, including head of the opposition Left Front group Sergei Udaltsov, have been detained by police.