"Hello, this is George W. Bush."

Darl McMahon isn't a personal friend of the president, so she was understandably startled to hear that greeting a few weeks ago as she answered the phone in her Mt. Lebanon home.

It wasn't the president, but it was his recorded voice.

"I'm calling to ask you to fill out your absentee ballot request form," the robo-call continued.

"I thought it was really funny, and a little unbelievable" said McMahon, who describes herself as a political independent. "The very next day I got the mailing."

Identical calls filled phone lines across the state in the waning days of summer. In person and by mail, hundreds of thousands of similar appeals are being made across the country in what is anticipated to be the largest mobilization of absentee balloting in history.

Curtis Gans, of the Committee for the Study of the American Electorate, estimates that between 20 and 25 percent of the votes in the presidential election will be cast before Nov. 2, either in traditional mailed absentee ballots or through early voting systems that have sprung up in some states. That compares to 15 to 20 percent in 2000. Figures on absentee votes are imprecise because of varied counting methods among the states.

The two presidential campaigns, abetted by an array of interest groups, are pouring resources into the competition for those votes. The anticipated increase in absentee votes could boost voter participation, but critics fear that it brings a commensurate increase in opportunities for abuse.

"In an election this close, with a shrinking pool of persuadable voters, no rock is being left unturned by the operatives on both sides," observed Dan Shea, who directs Allegheny College's Center for Political Participation. "You might say it's an opportunity to manipulate the system; on the other hand it's an opportunity to get more people to vote."

In Pennsylvania, the Bush campaign has mounted an early aggressive absentee effort with targeted mass mailings, including ballot requests.

"It's a massive operation statewide," said Mike O'Connell, executive director of the Allegheny County Republican Party. "The Bush campaign has been very active; they're far ahead of any place I've seen [campaigns] in the past."

The automatic call and mailer combination that McMahon received was one of hundreds of thousands directed to households across the state.

Tony Podesta, Sen. John F. Kerry's chief Pennsylvania strategist, said the Democrats are determined not to be outgunned in the absentee warfare, but, by early September, they had yet to finalize their tactics.

"We're in the middle of that conversation right now," Podesta said last week.

Union-funded retiree groups, acting separately from the Kerry campaign, have already begun courting absentee votes from senior citizens. Business groups, supporting Bush, have mounted similar efforts in Pennsylvania and across the country.

Ed Coyle, president of the Alliance for Retired Americans, a new group funded by a consortium of unions, has targeted Pennsylvania along with five other states for an intensive absentee ballot program.

"We have 250,000 members in Pennsylvania," Coyle said. "They've already received two issue pieces so far; all of them will get absentee ballot forms in the near future."

Groups allied with the GOP, such as the U.S. Chamber of Commerce and the Business-Industry Political Action Committee, are also prodding early voters. A Web site created by BIPAC, www.ezvote.org, provides downloadable ballot applications and other polling information across the country with the relevant information sorted by zip code.

These combined efforts threaten to alter the traditional concept of a national election day, in addition to affecting voter turnout. In 29 states, voters can cast ballots in election windows of varying duration, either through early voting at central polling places or so-called no-excuse absentee voting, in which absentee ballots are available to any citizen who cares to use them.

In Oregon, votes can be cast as early as Sept. 18. In Iowa, voting begins on Sept. 23, and in Florida, ballots can be cast starting Oct 18.

Gans is concerned that the increasingly extended voting period undermines the concept of an election as a collective national decision in that voters who go to the polls on Election Day may have more or different information about the candidates than those who vote early.

"In a national election, and especially a presidential election, all those who are casting ballots, save those who truly cannot come to the polling place on Election Day, should have the same information on which to render a judgment," Gans' center wrote in a recent report on early voting.

Gans' solution is simple. "Roll them back," he said, arguing that only those who are truly unable to go to the polls should be eligible for absentee ballots and that early voting systems should be discarded in favor of the traditional Election Day.

Gans also maintains that early voting systems create the potential for undermining the secrecy of voting, offering the scenario of groups on the right or left exerting pressure on voters to disclose their preferences.

Allegheny's Shea said he wasn't as concerned as Gans on the issue of absentee abuses, but he did share his unease over the drift away from a single national day of decision.

Pointing to one practical consequence of the newer timetables, Shea noted, "You're going to have many people voting before the debates."

In a study issued earlier this week, the Center for the Study of the American Electorate also reported the counterintuitive finding that early and liberalized absentee voting systems do not, as intended, increase turnout. To the contrary, the report found that states with early voting had a lower increase in turnout between the presidential elections of 1996 and 2000 than states with more traditional systems.

The report speculates that relative declines are due to the fact that some people may request ballots and then not return them. Another factor, affecting both absentee and early voting, may be that the extended voting periods force parties and other interest groups to spread their get-out-the-vote efforts over a longer period of time, rather than concentrating on one date.

In Pennsylvania, absentee ballots are legal only for voters who cannot make it to the polls for health reasons, or because they will be away from their municipality during polling hours. As a practical matter, however, Pennsylvania's system is not far removed from no-excuse absentee systems. Absentee ballots submitted on time are presumed valid, and it would be a herculean task to police them to weed out voters who went the absentee route simply because they felt like it.

Completed absentee ballots are sent to a voter's home polling place on Election Day and, unless challenged, at a cost of $10 per contested ballot, they are counted along with all other votes. The county election board is charged with ruling on challenges at a hearing in which the challenger, but not the voter, is required to attend.

Earlier this year, the state Supreme Court, responding to a Republican lawsuit, invalidated 56 ballots from the November, 2003 election because they had been delivered to the county elections division by third parties, rather than by the voters, either in person or by mail. The Republican plaintiffs expressed fears that Democratic Party workers could have been collecting votes en mass at nursing homes or other facilities.

Due to the ruling, county elections divisions will no longer accept ballots delivered by third parties, although a determined operative who had collected multiple ballots, at nursing homes, for example, could circumvent the rule simply by mailing the ballots separately.

Mark Wolosik, director of the Allegheny County elections division, said the pace of both new voter registrations and absentee ballot requests had significantly accelerated this year.

"Everything started earlier," he said. Pointing to the controversy over Florida's voting tabulation in 2000, he said, "Florida has increased the scrutiny over every aspect of the process and that's one of the reasons people are doing things earlier."

Since the beginning of the year, Allegheny County's voter registration has increased by more than 40,000. That's a much heavier than normal pace, but Wolosik said it was too early to determine whether it would end up being a record increase.