HOT SPRINGS, Va. — U.S. Senate aspirants Republican George Allen and Democrat Timothy M. Kaine went on the attack in a debate Saturday, signaling a change in the closely watched race as the two tried to appeal to crucial independent voters who will most likely decide the outcome.

Each accused the other of name-calling and partisan squabbling even as both tried to show they had worked with members of the opposite party — and could do so again in what has become an increasingly partisan Washington.

Allen criticized Kaine for serving as chairman of the Democratic National Committee during his last year as governor of Virginia. Kaine accused Allen of continuing to engage in “smash mouth” politics as he mentioned several Republicans with whom he had worked.

The contest to fill the seat of retiring Sen. James Webb (D) is expected to be one of the most competitive races in November, one that will help determine the balance of power in the Senate.

Allen defeated three lesser-known candidates to win his party’s primary last month, while Kaine ran unopposed. The two have remained deadlocked in polls for a year. A Washington Post poll in May showed them tied at 46 percent apiece among registered voters.

The former governors debated in front of hundreds of lawyers at the upscale Homestead resort nestled in the mountains near the West Virginia border. At least two former governors — Democrats Gerald Baliles and L. Douglas Wilder — and one hope-to-be governor, Attorney General Ken Cuccinelli, were in the audience.