PARIS Many overseas Americans - possibly thousands - may not be able to vote in this year's presidential election because of an omission during the latest round of U.S. electoral reform, according to U.S. officials and organizations representing Americans abroad.

Left out of the Help America Vote Act of 2002 were young Americans who have never lived in the United States but who do have U.S. citizenship through an American parent.

While some states allow these youths to register at the voting address of their parents, more than three-quarters of the states do not, leaving a significant slice of U.S. citizens abroad effectively disfranchised as they come of age.

"There is no federal legislation on this at present," said Polli Brunelli, director of the Federal Voting Assistance Program. "The states are the ones who administer elections. They pass the laws on voting."

Twelve states allow Americans who have always resided abroad and are children of U.S. citizens to use a parent's voting address, Brunelli said in a telephone interview from Washington. The states are Delaware, Georgia, Hawaii, Iowa, Massachusetts, New York, Oklahoma, Oregon, Rhode Island, Tennessee, West Virginia and Wisconsin.

As for the 38 other states, voting advocates say that the rules are diverse - so diverse, in fact, that it is not clear whether some states even address the issue of foreign-born and raised children of U.S. citizens.

So if the parents are registered in one of those 38 states, will first-time overseas voters be able to cast ballots in the Nov. 2 election?

"That's what they have to find out," said Glenn Flood, a spokesman for the U.S. Defense Department, which runs the Federal Voting Assistance Program. "They have to submit their application to register, and the state will tell them what the stipulations are."

The number of young voters who may be unable to exercise their right to vote is unknown, Flood said by telephone from Washington, because "we don't track U.S. citizens overseas."

There is no precise count of Americans abroad, although a U.S. census experiment is under way in three countries - France, Kuwait and Mexico - as a prelude to possibly including overseas citizens in the next full U.S. census in 2010.

Estimates vary. According to Flood, potential voters overseas - civilians, military forces and their families - number six million. Organizations representing Americans abroad put the number of civilians overseas at 4.1 million.

Of those, the number who have always lived abroad and have turned 18 since the last presidential election in 2000 - when overseas absentee ballots became an issue in the Bush-Gore count - is unknown.

"There could be thousands in that category," said Lucy Laederich, a Paris-based nonpartisan advocate for overseas Americans. "But of course we'll never know until we're counted in the census."

Barbara Stern, the Paris-based voting director of the Association of Americans Resident Overseas, said that many people had been asking this year about how to register their children.

"The problem about Americans overseas is that the numbers are wildly uncertain and nobody has cared," she said. "Now, with the interest in overseas voting, and increasing numbers of absentee overseas voters, there is interest in Washington in trying to identify who we are."

How much interest is open to question, however. When the U.S. Congress tackled election reform in the wake of the problems encountered in the Bush-Gore contest in 2000, "overseas voters were not even included in the Senate bill" until the day before its passage, when Senator John Rockefeller, Democrat of West Virginia, introduced an amendment, Laederich said.

Rockefeller and two New York congressmen, Representatives Tom Reynolds, Republican, and Carolyn Mahoney, Democrat, had sponsored earlier bills that did take account of the concerns of Americans abroad, with provisions to simplify state rules on voting, eliminate notarization requirements and collect data on overseas citizens.

But by the time the House and Senate reached a compromise and adopted the Help America Vote Act, some measures sought by overseas groups, including allowing Americans who have never lived in the States to register at the voting address of their parents, had fallen by the wayside.

The act, signed into law by President George W. Bush one week before the November 2002 congressional election, "was designed to ensure that each eligible citizen would have an equal opportunity to cast a vote and have that vote counted," said Veronica Gillespie, elections counsel with the Senate Rules and Administration Committee, who worked on the legislation.

However, she added, "the Help America Vote Act has as a guiding principle that it would not change the role of the states in conducting federal, state and local elections. This means the act did not introduce a federal law that governed eligibility requirements for voter registration, voting or counting votes. State law controls voter eligibility."

Brunelli, of the Federal Voting Assistance Program, said the program had asked the 38 states that have not yet done so "to pass legislation to enfranchise those U.S. citizens who have never resided in the States."

In the meantime, citizens abroad who find themselves unable to register may challenge their state law under a complaints process, said Gillespie, speaking by phone from Washington.

People who feel they have been disfranchised, she said, can turn to a law that will permit them to file a complaint with the relevant state.

Again, however, the modalities of the complaints are up to the states. While some may post regulations on the Internet, making them accessible to overseas voters, others may post them on the statehouse door - and there is no guarantee that a voter who files a challenge will win.

On the positive front, said Laederich, the advocate for overseas Americans, it has become easier since 2000 to get registration forms and request ballots online. For most states, the Federal Post Card Application needed to register as an absentee can be obtained at www.fvap.gov/pubs/onlinefpca.html.

Another advance is that the Help America Vote Act extended the registration period for overseas voters to four years, so that registering now for the Nov. 2 election will also entitle voters to cast ballots in the 2006 congressional elections.

Flood, too, spoke of a rebirth of citizen interest and said that many more people have been calling in this year for information from the Federal Voting Assistance Program. Toll-free numbers exist in 64 countries to allow Americans to contact the program, which can patch them through to their local voting district. The numbers can be obtained online at www.fvap.gov/services/tollfree.html.

fawco.org has a full panoply of information about voting for overseas Americans, with links to many other sites. www.fvap.gov is the official site of the Federal Voting Assistance Program.

www.census.gov/overseas04 is the U.S. Census Bureau's site for overseas Americans in France, Kuwait and Mexico who wish to take part in the February-July test census.