The long-standing practice of using a driver’s license, birth certificate or a simple verbal acknowledgment that you are an American citizen to re-enter the country from Mexico or Canada is nearly over.

Beginning in January, passports will be required of U.S. citizens traveling to and from those two countries and a few others in the Western Hemisphere that are popular destinations for U.S. tourists.

Americans already are flooding post offices and passport agencies with applications as they try to avoid a last-minute rush at the end of the year.

“Our applications have increased substantially – up to 30 percent in some cases over last year,” said Steve Royster, spokesman for the U.S. State Department’s Consular Affairs Bureau.

The rush for passports also is being felt at Lawrence’s main post office, 645 Vt.

Linda Beers, who handles passport applications, estimated about 4,000 applications were filed through the post office last year, but the number will be way up this year.

“Before I had gotten halfway through the year, I know I had done more than I did at the same time last year,” Beers said.

Effective Jan. 8, 2007, all American citizens traveling by air or sea to Canada, Mexico, the Caribbean, Bermuda or Panama must have a passport. That includes children of all ages.

“It doesn’t matter if you are 1 day old. If you are going to travel, you have to have a passport,” Beers said.

Currently, travel to these countries only requires a certified birth certificate and perhaps a driver’s license as a second form of identification to get back into the U.S. In some cases, it might even be as simple as travelers making oral declarations that they are American citizens, Royster said.

“Then it is up to the Customs and Border Protection agent to make a determination whether he believes you are entitled to be admitted into the U.S.,” Royster said.

Through 2007, passports still will not be needed if traveling to Mexico or Canada by land.

But that, too, will change, effective Jan. 8, 2008. Then a passport also will be needed for land travel.

The changes are being made on Jan. 8 to avoid complicating the holiday travel season preceding it, Royster said. The new rules are part of the Western Hemisphere Travel Initiative intended to increase U.S. security in the wake of the Sept. 11, 2001, terrorist attacks.

There are currently about 5,000 forms of identification someone could use to cross the border by land, Royster said.

“The border agent will have a single ID – a passport – to document someone,” he said.

Travel agencies are informing their clients of the new passport rules, but most clients of Travellers Inc., 831 Mass., already are aware of them, said Walt Houk, the firm’s president.

“We definitely tell them about it,” he said. “They need to plan well in advance. You don’t want to wait until December if you are going to travel in January.”

Travellers encourages its clients to make sure their passports have at least six months left before expiration in case unexpected problems arise. Some airlines have been known to refuse boarding for someone whose passport is near the expiration date, Houk said.

“On tours we usually ask clients to give us a photocopy of their passport so we can check to see when it expires,” Houk said. “If we see that there is any danger in it expiring anytime soon, we get right back in touch with them.”