If the battle for control of the Senate is as close as some analysts suggest, the outcome may not be known until Louisiana finishes voting, more than a month after the polls have closed everywhere else.

And if the outcome is close and Sen. John F. Kerry (D-Mass.) is elected president, the wait could be even longer -- possibly until late spring -- when a new Massachusetts law provides for a special election to choose Kerry's successor.

The Louisiana delay arises out of the state's unique election law, which calls for a runoff to be held Dec. 4 if no candidate receives more than 50 percent of the state's senatorial votes on Tuesday. If there's no decisive victory Tuesday, the outcome won't be known for a month -- which might affect the balance of power in the Senate.

As of the latest polls, Rep. David Vitter, the only Republican in the seven-man field running to succeed Sen. John B. Breaux (D), is edging toward the 50 percent mark. If he gets a majority, he will be the first Republican elected to the Senate from Louisiana since Reconstruction. But if he falls short, he will have to face the next highest vote-getter, most likely Rep. Chris John or State Treasurer John Kennedy. John narrowly leads Kennedy for the second-place spot, but both were running far behind Vitter in recent polls.

In a head-to-head contest with Vitter, Democrats believe their chances improve markedly. They point to recent runoff victories by two Democrats: Sen. Mary Landrieu in 2002 and Gov. Kathleen Babineaux Blanco in 2003. They also note that President Bush, who is running well ahead of Kerry in the state, will not be on the ballot in December.

Breaux, Landrieu and the Democratic Senatorial Campaign Committee are supporting John, and Vitter appears to be aiming most of his fire at him. Although John is one of the most conservative Democrats in Congress, Vitter is attacking him as a "Washington liberal." John says Vitter votes with Republican leaders 99 percent of the time and serves as their "puppet."

In Massachusetts, the legislature's Democratic majority pushed through a bill earlier this year aimed at assuring that Kerry's seat remains in Democratic hands if he goes to the White House. Without the new law, Kerry's successor would have been chosen by Gov. Mitt Romney (R) to serve until the 2006 elections.

The legislation requires the governor to call a special election to fill congressional vacancies within 145 to 160 days of receipt of a letter from the incumbent giving notice of his plans to leave office. Depending on when the letter is sent and when the governor schedules the election, the balloting could occur any time from late March to early July. At least half of the state's 10-member Democratic delegation in the House has indicated interest in a race for Kerry's seat.

Four years ago, control of the Senate remained in doubt after Election Day, but the issue was resolved a month later when Maria Cantwell (D) defeated former senator Slade Gorton (R) in a recount of votes from their race in Washington.

With Vice President Cheney casting a tie-breaking vote, the Senate remained in GOP hands until Sen. James M. Jeffords (R-Vt.) became an independent and aligned himself with the Democrats. In 2002, the GOP regained a 51-vote majority.