A vote could come as early as Wednesday night.
Even after months of intense lobbying by the president and administration trade officials, it was not clear if supporters had the needed votes.
Rep. Gil Gutknecht (R-Minn.) said Wednesday evening that he will vote against the proposed Central American Free Trade Agreement, making him the only Republican from Minnesota to oppose the deal.
"Unfortunately, when you compare the upside and potential downside, I believe the agreement has three potential fatal flaws," Gutknecht said in a statement. "They are fixable, but they couldn't be fixed before this vote."
Rep. Jerry Moran (R-Kan.) has questions about CAFTA and whether Central American trading partners may continue to erect barriers against U.S. products despite the agreement.
Moran also is using his vote as leverage to discuss other trade issues with the White House. When President Bush called Moran to the White House last week to talk about his vote, Moran urged the administration to ease restrictions on trade with Cuba and put more pressure on Japan to lift its sanctions on imports of U.S. beef.
Moran's Kansas colleague, Democratic Rep. Dennis Moore, traditionally a free trade advocate, remains concerned about the effect on U.S. jobs and whether labor standards would be enforced oversees, said spokeswoman Christie Appelhanz.
The agreement eventually would eliminate tariffs and other trade barriers between the U.S. and Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and the Dominican Republic. The trade deal was signed a year ago and approved by the Senate last month.
Kansas Republican Reps. Jim Ryun and Todd Tiahrt both plan to cast votes for CAFTA.
Opponents, mostly Democrats, blame free trade agreements for the overseas flight of American jobs and say labor rights provisions in the accord would perpetuate the exploitation of Central American workers.
Those fighting for passage say the agreement would open up markets for U.S. and manufacturers while making Central America's fledgling democracies more economically and politically stable.
U.S. exports to the region are modest -- currently about $15 billion a year. But the administration says it would be a mistake to turn away from a region just emerging from political turmoil.
"This is a small bill economically, but it is a big bill in terms of its impact," said House Democratic leader Nancy Pelosi of California.
"As our manufacturing base erodes, as our industrial base erodes, we have a president who is contributing to the further erosion of that base," Pelosi said.
Mr. Bush and Vice President Dick Cheney met for more than an hour on Wednesday with House Republicans to stress that a prosperous Central America was important to U.S. national security.
All except perhaps a dozen Democrats were expected to vote against the agreement. That is why the president and Republican leaders have concentrated on keeping Republican defections to a minimum.
Mr. Bush reminded Republicans that while some might oppose CAFTA for parochial interests, "we are here not only to represent our districts but to represent the nation," House Majority Leader Tom DeLay, a Texas Republican, said after the meeting.
To allay lawmakers' concerns about the U.S. sugar and textile industries, the administration has won over several Republicans by pledging protection from Central American imports.
Some textile groups now support the pact because it could help Central American clothing manufacturers, which buy large quantities of U.S. fabric and material, compete against Chinese goods, which have almost no U.S. content.
Mr. Bush has invested considerable time and effort to winning approval of CAFTA. For example, he invited the leaders of all six nations to a White House meeting, has spoken to Hispanic and business groups, and talked to dozens of lawmakers.