* Romney reminds voters of Gingrich's Medicare criticism
* Romney surrogates hint at Gingrich's marital troubles
* Gingrich supporter says criticism is sign of "panic" (Updates with Register board, campaign conference calls)
By John Whitesides and Sam Youngman
CEDAR RAPIDS, Iowa, Dec 9 (Reuters) - Republican Mitt Romney hit surging presidential rival Newt Gingrich on Friday over Medicare reform but left the toughest criticisms to surrogates who hinted at Gingrich's troubled marital past.
One day before a debate in Iowa, which holds the first contest in the Republican nominating race in less than a month, Romney also contrasted his business experience and leadership with Gingrich's "30 or 40 years in Washington."
"There's nothing wrong with that," Romney told the Des Moines Register's editorial board. "It's just different."
Gingrich, the former House speaker, has zoomed past former frontrunner Romney in recent polls in Iowa and nationally, prompting Romney and his campaign to ratchet up their attempts to raise doubts about Gingrich's record.
In a conference call for reporters, a top Iowa official of Gingrich's campaign said the tough talk from the Romney camp was a "load of crap."
"What we're seeing from Mitt Romney and Boston is desperation and panic," said Linda Upmeyer, Gingrich's Iowa campaign chairwoman and Iowa state House Majority Leader.
At his campaign stop in Cedar Rapids, Romney reminded voters Gingrich had attacked U.S. House of Representatives Budget Committee Chairman Paul Ryan's Medicare plan last spring as "right-wing social engineering."
Ryan's budget proposal, which would dramatically cut spending and transform the Medicare health plan for the elderly into a private insurance system, has become a popular cause for conservative Republicans.
"Speaker Gingrich and I have very different views in regards to Paul Ryan's plan and the need to fundamentally transform Medicare," Romney said after a town hall meeting inside an animal feed factory.
"My plan is not going to be identical to his but we are on the same page," the former Massachusetts governor said of Ryan's proposal.
Speaking to reporters later, Romney refused to discuss criticism of Gingrich by one of his surrogates, former White House Chief of Staff John Sununu, who called Gingrich "irrational" during a Thursday conference call sponsored by Romney's campaign.
'I DON'T WRITE THOSE SCRIPTS'
"My views are focused on the distinctions we have on issues and the reaction to the Ryan plan to reform Medicare," Romney said. "As for the comments of other folks who are supporting me, I don't write those scripts for them."
Romney also refused to discuss a web video by a political action committee supporting him called Restore Our Future that suggests Gingrich has a "ton of baggage" as a presidential candidate.
"I don't have any comment on anything that PACs are going to do or say," Romney told reporters.
In a campaign-arranged conference call on Friday, state representative Renee Schulte, a Romney supporter, focused on Romney's family and "life of integrity."
Pressed by a reporter, she said she was not trying to draw attention to Gingrich's two divorces.
"It's just a difference," she said. A Romney spokeswoman said on the call the campaign was not trying to draw attention to Gingrich's past.
On just his fourth trip to Iowa since the summer, Romney promised to be back more frequently in the last few weeks before the Jan. 3 contest opens the state-by-state nominating battle to find a challenger to President Barack Obama.
"You're going to see me more and more," he said. "This is heavy campaign time, I'll be in Iowa and New Hampshire a lot."
Romney has been ambivalent about his commitment to Iowa, where he lost in 2008 after spending millions of dollars. He did not compete in the state party's straw poll in August.
Iowa has a big bloc of religious conservative voters skeptical of Romney because of his past support for abortion rights and a healthcare overhaul in Massachusetts that became a model for Obama's national plan.
But Romney's attacks over the Ryan plan are designed to raise similar doubts about Gingrich among conservatives, although in a general election they could turn off independents who support Medicare as structured. (Additional reporting by Kay Henderson; Editing by Mohammad Zargham and Todd Eastham)