MIAMI - On a day the new Homeland Security Department wanted to trumpet streamlined and tightened border inspections for travelers entering the United States, the agency had to explain why undercover investigators had been able to cross into the country using counterfeit identification papers and bogus names.

The department said it would study the findings of the investigation by the General Accounting Office, which reported to a Senate panel that its agents had easily entered the United States with fake drivers' licenses, counterfeit birth certificates and other false documents.

Tom Ridge, sworn in last week as the first homeland security secretary, traveled to Florida yesterday to make a speech praising the border investigators who now work in his huge department. Ridge said the GAO operation raised "some legitimate issues that have to be resolved."

In testimony yesterday to the Senate Finance Committee, a senior investigator for the GAO, the investigative agency of Congress, said his colleagues had "entered the United States from Canada, Mexico and Jamaica through ports of entry using fictitious names and these counterfeit identification documents."

The investigator, Robert Cramer, said, "Immigration and Naturalization Service and U.S. Customs Service officials never questioned the authenticity of the counterfeit documents, and our agents encountered no difficulty entering the country using them."

The chairman of the committee, Republican Sen. Charles E. Grassley of Iowa, said the results of the investigation were shocking.

"Bouncers at college bars could spot the kind of fake IDs that were used by investigators," Grassley said.