* Republican feud over shutdown threat turns to name-calling
* Spat pits older moderates against Tea Party "young guns"
By David Lawder and Richard Cowan
WASHINGTON, July 30 (Reuters) - A nasty, name-calling spat between Tea Party conservatives and older, more moderate Republican senators is playing out in public this week, fueling a battle over the best way to kill President Barack Obama's landmark healthcare law.
Senators usually reserve for private conversations words such as "silly", "dumb," "dishonest" and "feckless" when referring to ideas being floated by members of their own political party.
But such constraints have been cast aside in recent days after a group of young, ambitious Senate conservatives including Marco Rubio, Ted Cruz and Mike Lee urged a government shutdown unless "Obamacare" healthcare exchanges are denied funding by Congress.
A must-pass spending bill has become the latest battleground for Republicans in their long-running attempts to kill the Democratic president's healthcare law. If Congress fails to approve new spending authority by the end of September, government agencies would shut down as the new fiscal year starts on Oct. 1.
Rubio, Cruz and Lee have persuaded nine other Republicans to join them in signing a letter to Senate Democrats pledging to oppose any appropriations bill that contains funding for the healthcare law.
They continue to seek more support but have been running into a wall of opposition within their own party.
"Oh, I think it's a silly effort," Republican Senator Bob Corker told MSNBC on Tuesday. "What people are really saying who are behind that effort is we don't have the courage to roll up our sleeves and deal with real deficit and spending decisions."
Corker joined moderate Republican Senators John McCain, Richard Burr, Lindsey Graham and Tom Coburn in sharply criticizing the defunding bid in recent days.
Seven-term Republican Senator Orrin Hatch of Utah said he feared Republicans would look "feckless" in pushing a doomed legislative strategy that some Democrats simply describe as "hostage-taking."
Graham, another senior Republican voice, said the strategy by the Tea Party - a loose political movement that seeks lower taxes and a smaller federal government - was "a bridge too far."
Several of these Republicans are involved in closed-door talks with White House chief of staff Denis McDonough to try to find a way to bridge profound disagreement between the two parties over budget issues.
Senator John McCain, calling the Obamacare defunding effort a "non-starter," said on Tuesday that the senators behind it were not around for past government shutdown battles.
Republican political fortunes suffered badly after they forced agencies to close in late 1995 and 1996 over funding levels, helping to seal the re-election of President Bill Clinton.
"It is a fact: When there is risk of a shutdown of the government, the Congress is blamed by the American people," McCain said.
But Cruz, a Tea Party firebrand from Texas who was elected in November, has showed no signs of backing down and on Monday labeled those criticizing his effort as "scared."
"What I can tell you is there are a lot of Republicans in Washington who are scared," Cruz said on conservative commentator Glenn Beck's radio show. "They are scared of being beaten up politically."
There have been 39 unsuccessful votes to repeal or undermine Obamacare in the Republican-controlled House of Representatives and a 40th vote is expected this week. Cruz said "our last and best chance" to stop Obamacare is to starve the fledgling program of federal funds needed to implement the law.
The core component of Obamacare - a requirement that uninsured Americans obtain health care coverage or pay a tax penalty - goes into effect in January 2014 but a first step is the opening of state-run online insurance exchanges in October.
Democrats argue that the mandate will bring down the cost of health insurance by expanding the risk pool but opponents claim it will cause insurance rates to rise and prompt businesses to drop their health plans, avoid hiring or cut employee working hours.
The effort to kill Obamacare will come to a head in September as Congress considers a funding measure. Under Senate rules, any senator can block legislation through a procedural tactic known as a filibuster. The only way to break the logjam is if 60 of the 100 senators vote to move the debate to a close.
It was unclear whether the "young guns" pushing to kill Obamacare would resort to a filibuster.