By Ros Krasny
BOSTON (Reuters) - Democratic Senate candidate Elizabeth Warren took the offensive against Republican Senator Scott Brown on Saturday, attempting to put questions about her ethnic heritage in the rear-view mirror with a fiery speech at a state convention.
Warren's attack came as two opinion polls showed the rivals locked in a tight race for Brown's Senate seat for Massachusetts, one of the most closely watched Congressional contests in the November election, in which the Democrats are seeking to protect a slim Senate majority.
"Scott Brown is a Wall Street Republican. A big oil Republican. A Mitt Romney Republican," Warren said at the Democrat's state convention in Springfield, Massachusetts.
"We have seen where the Republicans want to drive this country, and it is ugly."
As expected Warren -- who has a high national profile and has raised millions of dollars for her bid, much of it from out of state -- on Saturday officially became her party's nominee to face Brown. She won 96 percent of the vote in the nominating contest, avoiding a primary run-off.
The former official in President Barack Obama's administration, who is a professor at Harvard Law School, has faced weeks of controversy over suggestions she used distant Native American ancestry to help gain employment at top universities.
Brown's campaign has taken up the issue to question Warren's truthfulness and integrity.
"His answer is to talk about my family and to tell me how I grew up," Warren said. "Well, I say this, if that's all you've got, Scott Brown, I'm ready. And let me be clear: I am not backing down. I didn't get in this race to fold up the first time I got punched."
A poll published by the Boston Globe newspaper on Saturday showed Brown leading Warren 39 percent to 37 percent in a survey of 651 likely voters, within the margin of error of plus or minus 3.8 percentage points.
The survey was taken in late May, when the issue of Warren's Native American heritage was highlighted in local media.
In another poll released on Saturday, Western New England University, in a survey of 504 likely voters taken for the Springfield Republican newspaper, showed Warren with 45 percent to Brown's 43 percent.
An earlier poll by the university done in late February put Brown ahead by 8 percentage points. The margin of error for the new survey was plus or minus 4.4 percentage points.
The Globe poll showed that Brown, an affable politician whose voting record puts him among the most centrist Republican Senators, remains popular more than two years after his January 2010 upset win in a special election after the death of liberal icon Edward Kennedy. Brown's favorability rating was 55 percent. Warren's was 48 percent.
Speaking to the Democratic Party faithful, Warren invoked the memory of Kennedy, who held the Senate seat for more than four decades.
"It's a long way from Ted Kennedy to Scott Brown," she said, before cataloging a number of Brown's votes likely to enrage convention-goers. "We know where Scott Brown stands - and it is not with the people of Massachusetts."
Democrats see the Massachusetts seat as a prime target to pick up in the November 6 polls.
Democrats have a 51-47 advantage over Republicans in the 100-seat Senate, with two independents, but are defending more than 20 seats against Republican challengers in November, while Republicans are defending only about half that many.
(Reporting By Ros Krasny; Editing by Greg McCune and David Brunnstrom)