* Democrats' U.S. Senate super-majority at risk
* Republicans would be able to block legislation
* Obama efforts would need bipartisan support
By Thomas Ferraro
Jan 15 (Reuters) - U.S. President Barack Obama will face a far tougher fight advancing his agenda if a Republican wins Tuesday's special U.S. Senate election in Massachusetts.
On matters from healthcare reform to judicial nominees, Obama would no longer be able to prevail in the Senate with the support of only fellow Democrats. He would need at least one Republican -- and that could be difficult.
Obama is scheduled to campaign on Sunday in Massachusetts for Martha Coakley who is vying with Republican Scott Brown to replace the late Senator Edward Kennedy, a liberal icon who held the seat for nearly 50 years. [ID:nN15228424]
A Republican victory in this leading Democratic state would rock Washington and transform the political landscape ahead of the November congressional elections.
Here's a look at the issues if Democrats lose:
Democrats would lose their 60-vote Senate super-majority that now lets them clear Republican procedural hurdles and pass legislation or confirm presidential nominees without a single Republican vote.
If Democrats are stripped of such a majority, Obama would be forced to try to find common ground with Republicans, who have opposed most of his agenda, including his landmark bid to revamp the $2.5 trillion U.S. healthcare system.
A super-majority has not always been super for Democrats as they have often had difficulty sticking together and mustering 60 votes. But it would be a far more difficult if Brown becomes the 41st Republican in the 100-member chamber.
Democratic leaders are pushing to win final approval of a sweeping healthcare bill so Obama can sign it into law before a possibly victorious Brown is sworn in as a senator and is positioned to help fellow Republicans kill the measure.
It could take at least a couple of weeks for Massachusetts to certify the winner. Democrats may seek to delay the certification, while Republicans would likely push to accelerate it. Either way, expect a battle.
Democrats are certain to remind Republicans that they didn't rush the seating in the Senate of Al Franken, after a marathon court challenge of his razor-close race in Minnesota.
Franken gave Democrats their 60th vote. It marked the first time that either party had a filibuster-proof 60 senators since 1979, when Democrats had 61 and Jimmy Carter was president.
A Republican victory in Massachusetts could slam the brakes on a number of the president's efforts in Washington.
An already uphill battle to win passage of legislation to stem global warming would suddenly become much tougher.
Same with legislation to tighten regulation of the U.S. financial industry.
With the Republican Party shifting further to the right in recent years, Republicans considered moderate in the Senate have dwindled to Maine's Olympia Snowe and Susan Collins.
Democrats will likely target the pair for a possible 60th vote on a variety of matters, making Collins and Snowe king-makers.
That's what Democrats did earlier this year in winning passage of Obama's $787 billion economic stimulus package.
A Republican victory in Massachusetts, one of the nation's most liberal states, would be seen by many as a repudiation of Obama and his fellow Democrats in Congress.
A key issue in the race has been the healthcare legislation, which has proven to be highly unpopular.
Matt Bennett of Third Way, a political think tank, said the Massachusetts race "shows that moderates are unhappy with the direction of the country."
"Moderates are uneasy, angry, nervous," Bennett said, adding that they doubt that efforts in Washington on a host of fronts will do them any good.
While the Massachusetts race has energized Republicans, particularly grass-roots conservative activists, Bennett said the contest may also be a "wake-up call to Democrats."
Others might blame Coakley for running a lackluster campaign, much like the criticism Kathleen Kennedy Townsend suffered when she lost the 2002 governors' race in Maryland, another heavily Democratic state. She is Edward Kennedy's niece.
At the U.S. Capitol on Friday, Democrats were shaken by the thought of a Republican win in Massachusetts.
"The notion of Ted Kennedy's seat not being won by a Democrat is hard for many of us to swallow," said Democratic Representative Jan Schakowsky, adding that she is among those in the party who have sent money to Coakley's campaign.
Additional reporting by Richard Cowan; editing by Matthew Bigg and Vicki Allen