CONCORD, New Hampshire (Reuters) - A senior official in U.S. President George W. Bush's re-election campaign was sentenced to 10 months in prison on Wednesday for his role in suppressing votes in a key U.S. Senate race, a scandal that Democrats charge may involve the White House.

James Tobin, 45, one of three Republican campaign operatives convicted in a phone-jamming scheme designed to keep New Hampshire Democrats from voting in a 2002 election, was convicted in December of two telephone harassment charges.

Prosecutors had asked for a two-year sentence.

U.S. District Judge Steven McAuliffe described the crime as "extremely serious" and a threat to the U.S. political tradition of free and fair elections.

"People in your position need to know they cannot do these things and if they do the consequences are very, very serious," he said in handing down a sentence harsher than the six months home detention and community service sought by Tobin's lawyer.

Democrats want an investigation into 22 telephone calls made by Tobin and New Hampshire Republican Party officials to the White House on November 5 and 6, 2002, and say they believe national Republican officials may be involved in the scheme.

"I don't consider this sentencing to be the end of the matter. I consider this to be one more step in the process of uncovering exactly who knew about this," said Kathleen Sullivan, the New Hampshire Democratic Party chair.

"There are still unanswered questions," she said.

The national Republican Party, which has paid more than $2.5 million in legal fees to defend Tobin, has said the calls to the White House were routine during a tight state Senate race and had nothing to do with the phone-jamming.

800 HANG-UP CALLS

Get-out-the-vote hot lines set up by state Democrats and a firefighter's association to urge residents to vote were jammed by more than 800 hang-up calls. State Republican officials say they tried to stop it once they learned of the scheme.

Republican John Sununu beat then-Gov. Jeanne Shaheen in the election and state Republicans swept a number of close polls.

"This is going to continue to be an issue for a while," said Dean Spiliotes, director of research at the New Hampshire Institute of Politics.

He said it remained unclear why the national Republican Party spent millions of dollars defending Tobin.

"At first it seemed like he was a free agent working on his own with maybe one or two people. But then pretty quickly we saw that the Republican National Committee was spending millions to help with his legal defense. That shot us some pretty large red flags among people in the state," he said.

"Ever since then it's kind of grown slowly but surely. It hasn't gone away and I don't think it has peaked yet either."

Republican Party officials say they financed Tobin's defense because he had occupied a senior position in the national Republican Party when he was charged and because he had maintained his innocence.  

Tobin, the former New England regional director of the Republican National Committee, stepped down as New England chairman of Bush's 2004 re-election campaign when he became subject of a federal criminal investigation.

The former executive director of the New Hampshire Republican Party, Chuck McGee, was also convicted after testifying that he had come up with the idea for the scheme.

Allen Raymond, former president of a Republican consulting firm in Virginia, was jailed after admitting to arranging for telemarketing company to make the calls.

"We need to find out how high this goes in the Republican Party," said Paul Twomey, an attorney for the Democratic Party who is leading a separate civil lawsuit that alleges Republican voter fraud and seeks monetary damages.

Tobin was denied bail and also fined $10,000 and given two years of probation. He plans to appeal, his lawyers said.

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