In a presidential race whose outcome is expected to hang on turnout at the polls, an army of interest groups is pumping at least $350 million into get-out-the-vote campaigns that are rewriting the tactics of elections.

The efforts are part of the most expensive voter-drive ground war in history. It includes the major parties and their allies, the independent but partisan groups known as 527’s, whose attack advertisements have played a big role in both President Bush’s and Senator John Kerry’s campaigns.

And for the first time in a national campaign, it includes hundreds of civic organizations and deep-pocketed business interests.

These groups, including the United States Chamber of Commerce and coalitions of charities, are using millions of dollars from donors that the groups are not required to identify. And though the groups are nonpartisan, some emphasize issues identified with one candidate or the other.

The efforts include door-to-door drives, mass e-mailings and telephone campaigns intended for select groups of voters. And the onslaught has been heaviest in the states that are still up for grabs.

In Florida, for example, unions and civil rights groups are coordinating their efforts, dividing up the state by precinct to reach as many voters as they can. But the fervor has even reached Baghdad, where a Republican lobbyist is trying to help an estimated 100,000 employees of American contractors in the Persian Gulf vote in time to be counted.

Unlike the major parties and the 527’s, the nonpartisan groups are not bound by federal election law that requires them to say where the money comes from.

And unlike the major parties and the 527’s, the nonpartisan groups cannot promote a candidate or make political statements without endangering their tax status. But they can have much the same effect by emphasizing “hot button” issues that may tend to help a particular candidate, or by simply turning out groups that tend to vote overwhelmingly for one party or the other.

Voters have mixed reactions to the barrage. Many said in recent interviews that they enjoyed the opportunity for a bit of doorstep discourse with recruiters. But ot-hers said they were concerned about a loss of privacy and tired of being increasingly pushed to vote early by absentee ballot.

(By Permission, The New York Times)