By Sam Youngman
MYRTLE BEACH, South Carolina (Reuters) - Republican presidential candidate Mitt Romney, under increasing pressure to release his tax returns now, continued to resist that timetable on Tuesday and said he probably would not make them public until April.
Romney, the frontrunner for the Republican nomination to face Democratic President Barack Obama on November 6 and a former private equity executive with an estimated net worth of $270 million, has been reluctant to lift a curtain on his vast financial holdings.
In recent days, Romney's increasingly desperate rivals - namely former House of Representatives speaker Newt Gingrich and Texas Governor Rick Perry - repeatedly have questioned whether Romney, in not releasing the tax returns, is hiding something.
Their calls for Romney to release his returns were echoed on Tuesday in a New York Times editorial, which called Romney's "insistence on secrecy impossible to defend now that he appears to be closing in on the nomination and questions have intensified about his personal finances."
During Monday's Republican presidential candidate debate in Myrtle Beach, Romney said, "I have nothing in (the returns) that suggests there's any problem and I'm happy to" release them around the federal tax deadline in mid-April.
"I sort of feel like we are showing a lot of exposure at this point," Romney added. "And if I become our nominee, and what's happened (with past presidential candidates) is people have released them in about April of the coming year, and that's probably what I would do."
Tax analysts say Romney may have good reason to be reluctant to release his returns. For a person of Romney's diverse wealth, tax returns could show, for example, any strategies he uses to reduce his tax bills, such as any offshore partnerships that could serve as tax shelters.
Because a healthy portion of Romney's estimated annual income comes in the form of capital gains rather than a salary, it's likely that the tax rate on much of his income is just 15 percent -- the rate for capital gains -- rather than the 35 percent rate that the nation's top wage earners pay.
Romney acknowledged as much after a campaign event Tuesday in Florence, South Carolina.
He told reporters that his tax rate is "probably closer to 15 percent than anything."
Romney also said he gets speaker fees "from time to time, but not very much."
Annual campaign financial disclosure forms indicate that Romney was paid more than $374,000 in speaker fees between February 2010 and February 2011.
A SERIES OF ATTACKS
The demands by Gingrich and Perry are their latest attempt to draw attention to Romney's wealth and portray him as out of touch with the concerns of most Americans.
They also echo Gingrich and Perry's criticism of Romney's time at Bain Capital LLC, a private equity firm Romney co-founded in 1984 and left in 1999. Bain was involved in overhauling dozens of companies, and in some cases laid off thousands of workers.
Gingrich, Perry and others have portrayed Romney as a job killer and, as Perry put it, a "vulture capitalist."
The attacks don't seem to have worked. Romney is still riding high in public opinion polls of the Republican candidates. And some conservative Republicans accuse Gingrich and Perry essentially of an assault on capitalism.
Gingrich and Perry went after Romney on the tax return issue during Monday's debate, and Gingrich continued to pound on the theme Tuesday.
"It's interesting that Romney agreed that he ought to release his income taxes but he doesn't want to do it until April," by which time Romney could have clinched the Republican nomination, Gingrich said during an interview with CBS.
"I think the people of South Carolina ought to know now -- if there's nothing there, why hide it until April? And if there's something there, don't the people of South Carolina deserve to know before Saturday?"
Gingrich added that he would release his tax returns this week. As Texas governor, Perry has released his each year.
Gingrich and Perry are battling former Pennsylvania U.S. senator Rick Santorum to put together enough conservative votes to block Romney's march to the nomination.
Romney won the Iowa caucuses and New Hampshire primary this month - the first two nomination contests - and is favored to win the South Carolina primary Saturday as well as Florida's primary on January 31.
Santorum, thought earlier this month to be Romney's main challenger, has not been as vocal in calls for Romney to release his tax returns.
A Santorum aide said that he was unsure whether Santorum would press Romney on the matter, but said, "We've been a pretty staunch advocate of airing out all the laundry now."
"We don't need any surprises," the aide said. "We need to know now."
The Romney campaign dismissed the latest charge to release his tax returns as a sign of desperation.
"This is pasta politics," Eric Fehrnstrom, a senior Romney adviser, said. Gingrich is "throwing spaghetti against the wall to see what sticks."
(Editing by David Lindsey and Will Dunham)