Washington ? How long until Election Day? More than two months, you say — what remains of August, plus all of September and October and one day in November.

Wrong. The election starts well before Nov. 2. Voting begins in the battleground state of Pennsylvania on Sept. 13, barely three weeks from now. At least 17 other states will open their polls before the end of September. By Oct. 18, voting will have begun in all but six states. And in 29 states, you can vote early without providing any reason for your choice.

The early voting/absentee voting phenomenon is altering campaign strategies for both President Bush and Sen. John Kerry — and for independent groups supporting the rival candidates. The data just cited come from BIPAC, the Business Industry Political Action Committee, which has launched a major effort to mobilize member companies to persuade employees to fill out their ballots at their convenience, well before Election Day.

“Our message,” BIPAC’s Bernadette Budde said at a recent briefing, “is that Nov. 2 is the last day to vote.” The goal, she said, is to reach 20 million employees with mailings that include the voting records of the candidates on “business issues,” and thereby produce 711,000 extra votes in 18 target states.

The business side is far from alone in going after the early votes/absentee votes. When the Democratic National Convention met in Boston late last month, Iowa Gov. Tom Vilsack reported that his state party already had collected more than 30,000 absentee ballot requests.

“The beautiful part,” he explained, “is that you can track those ballots and keep on the people until you know they have filled them out and sent them in.”

The effectiveness of the technique was shown in a recent special election for the lone House seat in South Dakota. The seat, which had been held by a Republican, was won by Democrat Stephanie Herseth. As BIPAC’s Budde noted, more than 10 percent of the voters took advantage of the no-excuse absentee voting option. The remarkable thing was that of the 31,708 people who requested absentee ballots, 30,600 returned them. Herseth’s margin was 3,005 votes.

As more states have opened up their voting laws, more and more people have availed themselves of the option. Oregon is the only state where all elections are conducted through absentee ballots. But the custom has spread in California, where voters may request that they automatically receive absentee ballots for every election, and many other states from Arizona to Wisconsin, where no-excuse absentee voting stretches Election Day to a full month.

BIPAC cited Census Bureau statistics to show the potential for increasing turnout through early voting. In 2000, the post-election Census survey found that some 19 million registered voters did not cast ballots. Only 10 percent of them said out-of-town travel on Election Day was the problem. More than twice that number said they were too busy to vote and almost 15 percent blamed it on illness or some other unexpected emergency. Weather and transportation problems accounted for a few more.

By focusing on those non-voting but registered citizens, the barriers — real or imagined — to their casting ballots can be overcome, and elections can be won.

Of course, there are disadvantages to the early voting as well. People who fill out their ballots in September or early October do not have the full period of the campaign to inform themselves. There may be late developments — a debate performance or disclosure of something in the candidate’s record — that could cause them to switch their support.

A BIPAC memo offers suggestions of circumstances when a campaign ought to promote early voting. They include situations where the polling suggests the opponent is about to overtake the candidate, when some item of late-breaking negative news is anticipated or when some development gives the candidate “a temporary buzz.”

All this suggests that lengthening the voting period does not eliminate efforts to manipulate the results by rival campaigns. But signing up absentee voters is a healthy form of participatory politics, and when it comes to elections, the more participants, the better.

It’s a good thing both sides have discovered how to stretch Election Day into election weeks.

David Broder is a columnist for Washington Post Writers Group.