WASHINGTON, June 14 (Reuters) - A U.S. Senate committee on Thursday voted to put off until mid-2009 passport requirements for U.S. travelers entering the United States by land or sea from Canada and other neighboring countries.

The Senate Appropriations Committee unanimously approved the delay to June 1, 2009 because of a huge backlog in issuing new U.S. passports. That snarl followed another rule change -- tightening requirements for some air travel by U.S. citizens -- earlier this year.

The new passport requirement for land and sea travel, which would also mean Canadians traveling into the country will have to show passports or high-tech identification that can be scanned at borders, was supposed to begin on Jan. 1, 2008.

The full Senate is expected to consider the delay to the measure in coming weeks.

Congressional offices have been inundated by calls from constituents whose passport requests were caught up in a backlog as U.S. citizens scrambled to get passports.

Lawmakers say they have heard from people who waited months for their passports and were forced to cancel travel plans because of the problem.

Last week, the United States said it was relaxing rules for air travelers entering the United States from Canada, Mexico, Bermuda and the Caribbean just as the summer travel season was beginning. The Jan. 23, 2007, start of the passport requirement for air travelers was put off until October if travelers can show that they have applied for passports.

The U.S. began cracking down on border crossings after the Sept. 11 attacks on the United States.

Before then, for example, U.S. citizens freely crossed the 5,500 mile (8,900 km) U.S.-Canada border, often with no security checks. Those who were stopped could show passports, drivers' licenses, birth certificates or various other forms of identification.

In a June 11 letter to Secretary of State Condoleezza Rice and Homeland Security Secretary Michael Chertoff, two U.S. senators said more time was needed to prepare for the passport requirements.

The administration's insistence on putting the land and sea travel provision in place in January next year is "unrealistic and unachievable," wrote Patrick Leahy, a Vermont Democrat, and Ted Stevens, an Alaska Republican.

The U.S. House of Representatives wants more information on how well pilot projects worked before going ahead with the border-check program.

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