(Updates with campaign pledges in fourth paragraph.)

Dec. 29 (Bloomberg) -- Russian billionaire Mikhail Prokhorov said he will call new parliamentary elections next December in case he defeats Prime Minister Vladimir Putin for the presidency in March.

Prokhorov also said he would serve for only five years of his six-year mandate and make it easier for smaller parties to get into Parliament, according to the campaign program published on his website today.

Putin is facing the biggest protests of his 12-year rule over allegations of fraud in Dec. 4 parliamentary elections that gave his United Russia party a majority of seats. He has repeatedly refused opposition demands to hold a re-run vote.

Prokhorov said he would reduce to 3 percent the barrier for parties to gain seats under proportional representation in the State Duma, the lower house of parliament. He also pledged to allocate half of the 450 seats in the Duma for independent candidates and restore direct elections for governors, measures already promised by President Dmitry Medvedev.

--Editors: Paul Abelsky, Hellmuth Tromm

To contact the reporter on this story: Henry Meyer in Moscow at hmeyer4@bloomberg.net

To contact the editor responsible for this story: Balazs Penz at bpenz@bloomberg.net