AUSTIN, Texas (AP) - The two Republicans vying for Texas' U.S. Senate seat accused each other of lying about their records Monday on the eve of a debate that could feature even more mudslinging as the bitter campaign roars into its final two weeks.

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Tea party favorite and former state Solicitor General Ted Cruz said his opponent, Lt. Gov. David Dewhurst, lied about his record of cutting taxes while overseeing the Texas Senate since 2003 and accused him of attempting to cover up his past support of a guest worker program for illegal immigrants. Dewhurst countered that Cruz is misstating his legislative record and branded his opponent as a Washington-trained lawyer financed by Beltway insiders.

More fireworks were expected Tuesday at the studios of WFAA in Dallas when the candidates face off for their second and likely final debate.

Whoever wins advances to the November general election against the winner of a Democratic runoff between former state Rep. Paul Sadler and perennial candidate Grady Yarbrough. The Republican nominee will likely be heavily favored in the race to succeed retiring U.S. Sen. Kay Bailey Hutchison.

Dewhurst beat Cruz by 10 percentage points in the May 29 primary but failed to win a majority in a nine-candidate GOP field. Their July 31 runoff likely will be plagued by low voter turnout since many Texans could be on vacation or more worried about beating the summer heat than casting ballots.

The race is being viewed nationally as a key test of the tea party, and Cruz has won support from some of the movement's brightest stars, including Alaska Gov. Sarah Palin and South Carolina Sen. Jim DeMint. Dewhurst has been endorsed by Gov. Rick Perry, however, and nearly every Republican in the Texas Senate recently released a letter saying Cruz is misrepresenting the lieutenant governor's record working with the Legislature.

In a new television ad unveiled Monday, Dewhurst renewed his past claims that Cruz lied about helping his private, Houston-based law firm represent a Chinese company in an intellectual property dispute with an American tire manufacturer. It goes on to say that Cruz now is "lying about David Dewhurst."

"Cruz attacks Dewhurst on taxes and spending - false," an announcer says. "The record shows Dewhurst cut spending and taxes, opposed state wage, property and income taxes. And Ted Cruz, he's a lawyer trained in Washington. Half the money supporting Cruz comes from Washington."

According to filings with the Federal Election Commission, only between 30 and 35 percent of Cruz's contributions came from outside Texas. But Dewhurst spokesman Matt Hirsch said the ad's claim includes funds from outside groups supporting Cruz, including the Washington-based Club For Growth and the Senate Conservatives Fund.

Tallying those, plus what the Cruz campaign raised, show that 47 percent of all money spent on Cruz's behalf came from Washington organizations, Hirsh said.

James Bernsen, a spokesman for Cruz's campaign, responded: "I don't think there's a single thing in that ad that's true."

It comes after last week, when the Cruz camp acknowledged missing a deadline to file its financial disclosure reports. Dewhurst highlighted that in an internet ad called "What's Ted Cruz Hiding?," which also mentioned that Cruz once represented a Pennsylvania developer now awaiting sentencing in a scandal involving bribes to a judge.

Cruz fired back that Dewhurst had removed archives of his past speeches from his official state website, including a 2007 address where the lieutenant governor said he would support a guest worker program for illegal immigrants. The topic is especially sensitive since, in the days before the primary, Dewhurst released a radio ad making the dubious claim that Cruz "helps run two national organizations that have been leading the push to give amnesty to illegal immigrants."

Bernsen recalled the radio spot from May in responding to Dewhurst's latest ad: "This is the same man who attacked Ted by falsely saying Ted supported amnesty."

Both campaigns acknowledged that an abundance of attacks could hurt voter turnout, but blamed the other side for perpetuating them.

"It's not a back and forth," Bernsen said. "Everything we've done has been about the issues."

Hirsch said that "the difference is, we're talking about Texas and representing the interests of Texas, not about outsiders."

By WILL WEISSERT Associated Press

(Copyright 2012 by The Associated Press. All Rights Reserved.)