Is the Republican presidential race about to turn ugly?

Campaign advisers to Texas Gov. George W. Bush claimed that was the case yesterday after learning that rival Steve Forbes has begun testing possible lines of attack against Bush in a poll of Iowa voters, saying Forbes was preparing "trash-ball" and possibly erroneous ads against the GOP front-runner.

But Forbes advisers responded that the Bush campaign was prematurely crying foul to avoid a legitimate debate on the issues and said their candidate would not be deterred from forcefully and factually challenging Bush on his record.

Bush and Forbes, who finished first and second in the Iowa GOP straw poll on Saturday, have been eyeing each other throughout the campaign, and the argument that erupted yesterday represented an escalation in the tension between the two campaigns that has long been coming.

Four years ago, Forbes spent millions of dollars on television ads attacking Robert J. Dole, which left Dole permanently damaged in some states. Many Republicans -- particularly those allied with Bush -- have warned Forbes not to use the same tactic in this year's GOP fight. Forbes has argued that he never attacked Dole personally but has warned Bush that, if he doesn't want heat on the issues, "he should stay out of the kitchen."

Alerted to the Forbes polling by an Iowa supporter, the Bush campaign yesterday tried a preemptive strike against the wealthy magazine publisher, who has the financial resources to match the well-funded governor.

"We had certainly hoped we could take Steve Forbes at his word that he would not engage in [the] trash-ball politics of ugly attack ads that he did in 1996," campaign spokeswoman Mindy Tucker said. "He said he won't, but this is the same procedure he went through in 1996 before he launched a series of attack ads on Bob Dole."

Forbes campaign manager Bill Dal Col refused to discuss the poll or whether it was a prelude to negative television ads. He said the campaign routinely asks questions about all of Forbes's rivals, Republican and Democrat, and suggested that the Bush campaign was overreacting out of the concern that Forbes's candidacy was gaining strength.

"If they're paranoid and uncomfortable over their poor showing on Saturday [in the straw poll], that's their problem," Dal Col said. "I don't discuss what's in or not in a poll. I will tell you absolutely we're polling. On issues and issues only and [our] likely opponents' issues."

The poll came to light after a Bush county chairwoman in Iowa was telephoned for the survey Tuesday. She made rough notes of the questions and passed the information on to the Bush campaign, which made it available to reporters yesterday.

According to Charise Schwarm, the poll probed Bush supporters to determine whether they would be less likely to support him after being told about aspects of his record on taxes, judicial appointments and Taiwan and about a controversy over Texas funeral home regulation.

The Bush campaign claimed, however, that some information offered to voters in the poll was incorrect. Schwarm said that in one question, it was asserted that Bush had pledged not to raise Texans' taxes but later raised state sales taxes. Tucker said the question spread false information. "He supported a bill that was a net tax cut," she said.

In 1997, Bush supported a major restructuring of the Texas tax code, which included a big property tax cut but increased sales and other taxes to make up some of the lost revenue. In the end, the bill was rejected and the legislature approved a $1 billion cut in property taxes.

But Forbes pollster John McLaughlin, in a preview of the coming debate between the two candidates, said Bush "did propose a sales tax increase," although it was defeated. "He did not raise taxes," McLaughlin conceded. "It was defeated in the state Senate." He argued that senators who opposed the measure "didn't think" it was a tax cut.

"They keep trying to attack Steve and they're extremely frustrated because his positive message is catching on," McLaughlin said. "They're trying to run a campaign where they don't want to be specific and don't have to give details on issues and don't have to debate."

"I don't think there's any problem with an open debate about issues," Tucker said. "But what the Republicans and America will not take kindly to is the kind of attack ads he launched last time."

Tucker was asked whether the Bush campaign conducts polling or focus groups to ask about opponents' records. "We will not be asking questions about other Republicans," she said, adding, "We may test how their negative attacks on us are seen by people."

Yesterday's exchange came as the Forbes campaign shifted into a new phase, designed to engage Bush on issues and convince GOP voters that the nomination fight has become a two-person contest between the top two finishers in the Iowa straw poll.

Forbes spokesman Greg Mueller said the straw poll marked the culmination of a months-long strategy designed to correct the mistakes of Forbes's 1996 campaign and put him in position to challenge Bush directly for the nomination.

"We've emerged as the conservative candidate in Iowa and, I would argue, nationally," he said. "Two, we emerged as the main challenger [to Bush] in a more general sense. Three, we are clear and away the issues candidate. We've got the best candidate who's got the deepest and broadest reach."

But other Republicans said Forbes failed to accomplish everything he had hoped for in Iowa. "His showing in Ames was the first step in putting him on the path to becoming the alternative, but it's a long, long path," said Scott Reed, who managed Dole's campaign four years ago. But Reed said Forbes still has to make a "huge leap" to convince GOP voters he can win the presidency.

Rich Galen, a Republican strategist, said, "They didn't get what they wanted out of Iowa. They wanted to say it was a two-person race, and they can't say that."

Forbes ended up closer to third-place finisher Elizabeth Dole than to Bush, meaning he still will have to contend with her candidacy and that of Arizona Sen. John McCain, who skipped the Iowa poll. And with conservative activist Gary Bauer running fourth in the straw poll, Forbes faces competition to claim the mantle of the favorite of religious and cultural conservatives.

Forbes has spent considerable time and money building organizations in the early primary and caucus states, which he did not do four years ago, when he relied entirely on television ads. He also has continued to reach out to social and religious conservatives, a weak constituency for him four years ago.

The next step for Forbes is the launch of his new book, "A New Birth of Freedom," a campaign document designed to reinforce the idea that his is the most substantive GOP campaign and that he is prepared to talk about issues on which Democrats normally have an advantage: education, Social Security, health care, even the environment.

"That takes Forbes from the flat tax and his pro-life position to being a populist Republican," Dal Col said.

Forbes spent about $10 million nationally on a summer ad campaign, and a new round of ads is likely in the fall. Reed suggested Forbes may have to choose between targeting Bush and attacking his other opponents to force an eventual two-person race.

Forbes's advisers remain coy about the content of future ads. "I'm not going to say we're not going to get into a discussion of what positions the other candidates have taken," Mueller said. But he made clear the campaign wants to engage Bush soon, asserting, "Once we get Bush in debate, we think he's on our turf."