Washington ? As the Republican presidential candidates gather this morning in Des Moines for their fourth debate, Iowa GOP voters are expressing limited enthusiasm for the field of current and potential aspirants, according to a new Washington Post-ABC News poll. Their views appear to be a microcosm of GOP sentiment across the country and point to a wide open battle for the nomination.

Former Massachusetts governor Mitt Romney has emerged as the early leader in the campaign for Iowa. But his support is both soft and shallow, suggesting that the Republican race in the state, as nationally, remains extremely fluid.

Just 19 percent of likely GOP caucus attendees said they were “very satisfied” with the field of candidates – far below satisfaction levels among Iowa Democrats – and poll respondents were badly fractured when asked to rate the candidates on political and personal attributes.

Romney’s lead is built in large part on perceptions among Iowa voters that he has worked the state far harder than any of his rivals. Yet, despite the time, money and television advertising that Romney has showered on the state, former New York City Mayor Rudy Giuliani is seen as similarly electable, as experienced and about as strong a leader as the former Massachusetts governor.

Compounding an already muddled picture is the fact that former Tennessee Sen. Fred Thompson, not yet an announced candidate, is running about even with Giuliani, though he lags well behind other top candidates on many personal and political characteristics.

Arizona Sen. John McCain, who is struggling to rebuild his candidacy after the early July exodus of much of his top staff and his continued money woes, is now well off the lead in Iowa. Iowa Republican strategists said his support for comprehensive immigration overhaul badly hurt him in the state.

In the Post-ABC News poll, Romney led the field with 26 percent, with Giuliani at 14 percent and Thompson at 13 percent. About four in 10 Romney supporters said they back him strongly, however, and three in 10 of his supporters said they are “very satisfied” with their choices.

The poll showed McCain and former Arkansas Gov. Mike Huckabee tied at 8 percent, followed by Kansas Sen. Sam Brownback and Colorado Rep. Tom Tancredo at 5 percent, former Wisconsin governor Tommy Thompson at 4 percent, Texas Rep. Ron Paul at 2 percent and California Rep. Duncan Hunter at 1 percent.

There was limited interest in a possible candidacy by former House speaker Newt Gingrich, who has talked about running for much of the year. If on the list of candidates, he would register 4 percent.

The poll was conducted by telephone between July 26 and July 31 among 402 likely Republican caucus participants. The margin of sampling error is plus or minus five percentage points.