By TIM WEINER
 
MEXICO CITY, June 15 - President Vicente Fox said Tuesday that he would ask Congress to allow millions of Mexican citizens living abroad to vote for president in 2006.

"One citizen, one vote - it's the basics of democracy," said Mr. Fox, who cannot run for re-election.

His proposed law would cover all Mexicans living outside the country. Almost all - at least 10 million - live in the United States. Because many are illegal migrants, the precise number is unknown. The law now compels them to return home to vote. Few have in the past.

Mr. Fox has called Mexicans working in the United States heroes, mostly for the money they send home - an estimated $13.3 billion last year. Those remittances are Mexico's second largest source of foreign revenue, after oil.

Political analysts here calculate that a million or more new voters may cast their ballots, and Mr. Fox is courting every one of them closely. He is scheduled to travel this week to Chicago, Minneapolis and Detroit, where many Mexican-Americans and Mexican migrants live.

Mr. Fox, who leads the pro-business National Action Party, won election in 2000. He was the first outsider to defeat the ruling Institutional Revolutionary Party since 1929.

All three of Mexico's major political factions, including the left-leaning Party of the Democratic Revolution, support some form of legislation to allow Mexicans abroad to vote for president. All three will contest what now looks to be a wide-open presidential campaign.

Mexican politicians have been debating the issue of the migrant vote since at least 1988. One open question is whether voters would have to return home to register, or whether they could vote in Mexican consulates. Tighter United States border controls and visa laws instituted under antiterrorism laws would make it harder for both legal and illegal migrants to register in person in Mexico.

Mr. Fox said extending the right to vote to Mexicans abroad would be "an enormous step toward building a truly democratic Mexican society, toward ending an unjust form of political discrimination."

"Mexico is surely indivisible," he said. Its spirit "abides in the heart and knows no time or distance."

A right to vote for Mexican migrants, Mr. Fox said, would "honor the dignity of that part of our nation which lives and works outside our borders."