AMES, Iowa (AP) _ Former New Jersey Sen. Bill Bradley said Sunday his Democratic presidential campaign is gaining steam because he refuses to attack rival Al Gore.

Bradley, knocking on doors and mingling in back yards, said voters have grown weary of negative assaults, and are likely to punish candidates running that kind of campaign.

``I think that's where the American people are today,'' said Bradley.

While the vice president has held a lead in national polling, Bradley has narrowed the gap in key states like Iowa and New Hampshire and has made the race competitive.

Gore has responded by becoming more aggressive in his criticism of Bradley, who made it clear he won't respond. He said he wants, instead ``to project a positive vision.''

``It's been working,'' insisted Bradley.

On Sunday, Bradley went door-knocking in a tree-lined middle-class neighborhood, mingling with residents preparing for Halloween festivities.

``I've done a good amount of (door-knocking) running for president,'' said Bradley. ``It's a way of paying respect. If you do it with some, you are doing it for all. If you never do it then you aren't paying that type of respect.''

With much of the Democratic Party's establishment in Gore's camp, Bradley was seeking support among college liberals from nearby Iowa State University using issues like his call for expanded health coverage.

Aides were quick to point out that the 50 people who gathered in a back yard Sunday to hear him speak are not traditional party activists, but newcomers to the political process.

There were some signs that Bradley insistence on avoiding verbal fighting with Gore was getting some support.

``We very much appreciate your efforts to keep the campaign civil,'' said Michael Mendelson, who answered one of the doors Bradley knocked.

In addition to narrowing the gap in some of the polling, Bradley has made himself competitive with the vice president financially, raising enough money to keep the contest going deep into the primary calendar.

``I consider this a joyous journey,'' said Bradley.