WASHINGTON — President Bush on Monday sent Congress a controversial free trade agreement with Colombia — a move that will force lawmakers to vote within 90 days.

The agreement, which would tear down trade barriers between the two nations, is heavily opposed by Democrats in Congress.

Democrats contend that Colombia has not done enough to halt violence, protect labor activists and demobilize paramilitary organizations. The president disagrees, saying Colombia has addressed the issues.

"If Congress fails to approve this agreement, it would not only abandon a brave ally, it would send a signal throughout the region that America cannot be counted on to support its friends," Bush said.

The letter Bush signed in the Eisenhower Executive Office Building transmitted legislation implementing the trade pact to Congress. Lawmakers won't formally receive it until they return on Tuesday.

Bush's action will force Congress to take up the proposal under a fast-track process that will require votes within 90 days. Officials said Bush is acting now in order to force a vote before Congress leaves in the fall for the campaign season.

Bush, who has staked out free trade as one of his top legacies, is also hoping to win congressional approval before he leaves office on pending free trade agreements with Panama and South Korea.

Bush's action came one day after Mark Penn quit as Sen. Hillary Rodham Clinton's chief campaign strategist after it was reported that he had met with Colombia's ambassador to the United States to discuss the free trade agreement, which Clinton opposes.

The president said that during the 16 months since he signed the trade agreement, his administration has led trips to Colombia for more than 50 members of Congress, and has held more than 400 consultations, meetings and calls to push for its approval.

Bush said the deal with Colombia, a strong U.S. ally in the Western Hemisphere, is important for national security reasons. He praised President Alvaro Uribe is committed to democratic values and that since 2002, Colombia has reported declines in kidnappings, terrorist attacks, murders and violence against union members.

"Despite this progress, Colombia remains under intense pressure in the region," Bush said. "It faces a continuing assault from the terrorist network known as FARC, which has seized hostages and murdered innocent folks, including Americans, in an attempt to overthrew Colombia's democracy."

He said Colombia also faces a hostile, anti-American regime in Venezuela, which has met with FARC terrorist leaders and deployed troops to the Colombian border as a means of intimidating the Colombian government and its people.

"The need for this agreement is too urgent, the stakes for our national security are too high to allow this year to end without a vote," Bush said.

Associated Press Writers Deb Riechmann and Ben Feller also contributed to this report.