y JUAN FORERO

BOGOTÁ, Colombia, June 30 - As the White House lobbied Congress to win support for a Central American trade pact, the United States Labor Department tried for more than a year to block the release of reports that harshly criticized labor standards in the region.

The reports, by a labor advocacy group, the International Labor Rights Fund, were commissioned by the Labor Department, and concluded that working conditions in five Central American nations and the Dominican Republic were dismal, and that enforcement of labor laws was weak.

In a statement Thursday, the Labor Department called the findings biased and flawed. Dirk Fillpot, a spokesman for the department's Bureau of International Labor Affairs, said the study was "rife with unsubstantiated and unverifiable claims, questionable statistical data, and biased statements of findings and conclusions."

The Labor Department's condemnation drew a quick rebuke from Senator Byron L. Dorgan, a North Dakota Democrat. "The reports describe labor conditions that would be harmful, not helpful, for passage of Cafta," he said, referring to the Central American Free Trade Agreement. "So they decided to deep-six it."

The Associated Press first reported the developments Wednesday. The Senate voted to approve the trade pact on Thursday.

Representative Sander Levin, a Michigan Democrat, said the Labor Department should have permitted lawmakers to review the reports and make up their own minds.

The Labor Rights Fund concluded in nearly 400 pages that while there were some adequate labor laws in Central America, there were systematic barriers to enforcing those laws. Recordkeeping is shoddy, giving workers little chance to make claims against employers, the reports said, and sanctions for violations are weak.

The fund also found problems ranging from discrimination against labor organizers to inadequate measures against child labor. El Salvador, for instance, the study found that it was not uncommon for foreign companies to close shop and leave without paying workers. The study also noted a failure to maintain safety, citing two accidents at a textile plant in 2002 in which 560 workers were overcome by fumes in chlorine spills. The ensuing investigations were shoddy, the study found.

Though the Labor Rights Fund has been critical of labor standards in developing countries, the Labor Department nonetheless chose it to conduct the studies. The contract was worth $937,000. "We transparently and in good faith put in a proposal," said Bama Athreya, deputy director of the Labor Rights Fund.

But after the reports were submitted in early 2004, the Labor Department held them in secrecy, preventing their release to Congress and forbidding the fund to publish them, Mr. Levin, the Michigan representative, said.

Mr. Levin repeatedly requested that the reports be released, and the Labor Department released them in April. A central argument in the reports - that enforcement of labor standards in Central America is often nonexistent - is an important point of contention.

Opponents of Cafta say the United States should not trade with countries where worker rights are violated, while supporters say Cafta will help put teeth into enforcement efforts.