Toyota officials sought to develop a public relations campaign to attack the credibility of

key witnesses who have testified before Congress about acceleration problems with the company's cars, according to documents provided to the House committee investigating the automaker, The Washington Post reported.

The effort was based in part on polling conducted for Toyota by Joel Benenson, President Obama's chief pollster. His poll questioned the integrity of the witnesses: Sean Kane, a Massachusetts safety consultant, and David Gilbert, an auto technology professor at Southern Illinois University Carbondale.

Congressional investigators have demanded to know from company officials whether a campaign to debunk or discredit their witnesses was put into action.

The company says it never produced advertisements based on the polling. Still, plans for the campaign have drawn the ire of the House Energy and Commerce Committee, which, upon learning of them, told the automaker to hand over all related documents.

Lawmakers "would take very seriously any effort to malign or intimidate witnesses who cooperate with our investigations," a committee spokesman said in a statement Friday.

In November, Toyota announced that it would replace accelerator pedals on about 4 million vehicles in the United States because they can get stuck in floor mats, causing

unintended acceleration. The problem has been linked to as many as 39 deaths.

In news coverage and in public testimony, Kane and Gilbert have been highly critical of Toyota's response to the acceleration issue.

Kane works with victims' lawyers and runs a blog that is critical of Toyota. Gilbert testified to Congress in February that he had conducted an experiment showing a flaw in the electronics of a Toyota engine that could explain some of the incidents of unintended acceleration. The company has denied that electronics are a factor.

In a statement Friday, Toyota said Gilbert and Kane had made "assertions" that had "created unwarranted consumer concern."

"Toyota, like most organizations, conducts regular public opinion research," the company said, adding that Benenson had "tested for the widest range of potential messages to measure effectiveness."

Political candidates and companies often use polling to test the weaknesses of their critics or opponents. Benenson's survey, titled the "Kane/Gilbert Debunking Message Test," directed pollsters to read several negative statements about Gilbert and

Kane. The survey noted that a study Kane had commissioned from Gilbert was "nothing more than a manufactured stunt -- a parlor trick that would affect nearly all cars the same way, not just Toyotas." Having heard that, respondents were asked to say

whether that changed their opinion of Kane's and Gilbert's credibility.

Benenson declined to talk about the matter, saying, "We have been doing work for Toyota for three years, and we don't discuss publicly the work we do for any clients."

Rep. Henry A. Waxman (D-Calif.), committee chairman, sent a letter to Toyota's president in late March demanding "all documents" relating to the poll. The matter is expected to be made public in a hearing next week.

Attorneys for Toyota responded to the committee in an least two letters. In one dated April 9, the company's top lawyer acknowledged that Benenson's survey results were used "primarily to guide the company's advertising development efforts. Ultimately, Toyota chose not to place advertising relating to this issue."

In their second response, on April 28, company officials cited a letter from Benenson submitted to the committee in which the veteran pollster said that "testing messages to rebut unfair or false assertions is a common and legitimate research practice and is no different than message testing our firm regularly does for Congressional candidates or Congressional campaign committees in response to critics or opponents."

According to documents provided to the committee, Toyota received advice about how to respond to Kane and Gilbert from Benenson and New York public relations firm Robinson, Lerer & Montgomery. The documents show that Benenson's firm, Benenson

Strategy Group, has conducted 25 surveys about Toyota's reputation since December 2009.

On Friday, Kane said he considered the automaker's attempts to discredit him as validation.

"If we weren't finding something that was meaningful, they wouldn't be spending this kind of time and money," he said in an interview. "But what we're seeing is that they're willing to go to great lengths to discredit anyone who asks questions about their products."