KIEV (Reuters) - Ukrainians voted for a new parliament on Sunday in an election that President Viktor Yushchenko said offered a choice between "false stability and change" after months of political turmoil.

The pro-Western Yushchenko, swept to power in the 2004 "Orange Revolution," has been sharing power grudgingly with the man he defeated in that upheaval, Viktor Yanukovich, who has bounced back to challenge him as prime minister.

The president has rejoined forces with Yulia Tymoshenko, a former premier who roused vast orange-clad crowds in the "Orange Revolution," sparked when an election was rigged to ensure Yanukovich became president.

"The choice is between two alternatives -- false stability and change," the president said alongside his wife and daughter at a polling station in central Kiev, bathed in warm sunshine.

"And I believe the nation will opt for change."

Yanukovich's campaign has stressed stability and economic growth of 7.1 percent in the ex-Soviet state of 47 million last year. Casting his ballot in Kiev, he said voters would decide "just who is more pragmatic."

Tymoshenko, speaking in her home town, Dnipropetrovsk, said an "Orange" team would waste no time if it won: "We know that we will have to accomplish 10 days' work in a single day."

Polling stations to elect the 450-member assembly were to close at 10 p.m. (1900 GMT). Exit polls will immediately be made public, with official results available from Monday morning.

Turnout stood at 43 percent by 1300 GMT and was expected to clear the 50 percent required to validate the poll. Voters cast ballots with few of the queues or other difficulties that plagued previous post-Soviet elections.

Reforms and policy initiatives have stalled over the last year as president and prime minister bickered. Confusion over contradictory orders was compounded by ill-defined changes to presidential powers.

COALITION TALKS

Polls say no clear winner will emerge in the election, called by Yushchenko after he accused Yanukovich of an illegal power grab. Long talks to form a coalition are almost certain.

Differences in orientation towards the West and Russia, key in 2004, are all but absent. Yanukovich, backed then by Russia, now describes himself as pro-European and focuses mainly on the living standards of voters earning on average $260 a month.

"Orange" parties were still likely to win most support in the nationalist west, the centre and Kiev, while Yanukovich's power base remains in the largely Russian-speaking east.

"The main thing is stability and calm, no fuss," said businessman Igor Krivosheyev, who voted for the Regions Party in Donetsk, its eastern stronghold. "Things were crazy with an Orange government. Legislation, taxation -- always changing."

In Kiev, Yuri Maximov, 49, backed Tymoshenko's pro-Western agenda. "This will bring us closer to Europe. This is probably a unique chance when I can change something by voting."

The last opinion polls, dating from two weeks ago, showed Yanukovich and his Communist allies just ahead of the combined tally of the pro-presidential Our Ukraine and Tymoshenko's bloc.

Only one other bloc among 20 entries, headed by centrist former parliament speaker Volodymyr Lytvyn, is given an outside chance of clearing 3 percent of the vote to win seats.

Tymoshenko is almost certain to become prime minister if the Orange camp wins. She was Yushchenko's first premier in 2005, but he sacked her amid debilitating infighting in her team.

Yanukovich has not ruled out a "grand coalition" between his Regions Party and Our Ukraine, a scenario favored by several economic analysts that would shut Tymoshenko out of government.

(Additional reporting by Lina Kushch in Donetsk)