The Supreme Court finished questioning witnesses and examining evidence yesterday and opened the floor for debate before adjourning for the day.
Hundreds of opposition supporters are gathered near the court house in Kyiv to await the ruling, which could come as early as today.
Under Ukrainian law, the Supreme Court cannot rule on the overall results but can declare results invalid in individual precincts.
Both Yushchenko and Yanukovych have pledged to honor the Supreme Court's decision.
Outgoing President Leonid Kuchma said he would be willing to dismiss the government if powers are first transferred from the president's office to the prime minister and parliament. The parliament passed a nonbinding vote of no confidence in the Yanukovych government on 1 December.
"The [proposed] constitutional reform will practically allow us to approve a government formed by the parliament, in accordance with the new law, so in that case the parliament and the government will assume responsibility for the situation in the country," Kuchma said.
Consulting With Moscow
Kuchma was speaking after talks with Russian President Vladimir Putin during an unscheduled visit to Moscow.
During those talks, held at an airport outside Moscow, the Russian leader -- who had receded from the debate in recent days -- said a repeat of the 21 November runoff would "yield nothing."
Putin instead backed Kuchma's call for a fresh election with new candidates and emphasized the traditionally close ties between Moscow and Kyiv.
"We express our support for everything you are doing to strengthen the country and to find a way out of the crisis, and I want to assure you that Russia will always be with Ukraine and will always support and help Ukraine in all its efforts aimed at stabilizing the situation in the country," Putin said.
Kuchma and Putin both backed Prime Minister Yanukovych's presidential bid.
In Washington, U.S. President George W. Bush said any new voting should be open, fair, and free of foreign influence.
The Court Decision
There are questions about whether the Supreme Court itself will hand down a fair verdict.
But Volodymyr Vassylenko, a Ukrainian legal expert, said there was no evident bias in any of the court's decisions on smaller election issues following the first round on 31 October.
"When this election campaign started, the Supreme Court was involved in the resolution of several cases related to the election campaign. And in my opinion, the court did quite well in delivering objective decisions," Vassylenko said.
It is still unclear what will happen once the Supreme Court makes its ruling.
RFE/RL Ukraine analyst Roman Kupchinsky said that even an "illegal" ruling might do little to change the current standoff.
Such a decision would send the process back to Kuchma, who can order fresh elections by presidential decree. But Yushchenko has stated repeatedly he would agree only to a second runoff and not to an entirely new vote.
With no political resolution likely, Kupchinsky suggested, the decision could ultimately come down to the will of the Ukrainian public.
Such a scenario would presumably work in Yushchenko's favor. Hundreds of thousands of opposition protesters have gathered in the capital for daily demonstrations since the runoff.
Yushchenko last night told supporters gathered in Kyiv's Independence Square that Kuchma and Yanukovych -- Kuchma's first choice of successor -- might be willing to resort to police action in order to hold on to the presidency.
"We know that whatever the extent of falsification of the 21 November election, they would have never won this election. So the use of force was and remains one of the key scenarios in Kuchma and Yanukovych's behavior," Yushchenko said.
[Click here for more RFE/RL coverage of Ukraine's disputed presidential election.]