Agriculture Department officials acknowledged yesterday that the agency quietly and improperly allowed millions of pounds of Canadian "processed" beef into the United States, despite an often invoked ban against importing that type of meat.

"Clearly the process and our failure to announce some of these actions was flawed," said W. Ron DeHaven, the USDA's chief veterinary officer. He and other top officials said, however, that the decision to allow in selected Canadian processed beef was "scientifically sound" and that the meat was safe.

A ban on Canadian beef was put in place last May after mad cow disease was found in the Canadian cattle herd. It was reaffirmed for processed beef when USDA Secretary Ann M. Veneman relaxed restrictions on some other Canadian beef products in August.

Yesterday's acknowledgement came after a private USDA briefing at which Republican and Democratic lawmakers took the agency to task for allowing some companies to import processed beef -- usually defined as ground beef, hamburger patties, cubed beef and sausage -- while those products were officially banned.

House Agriculture Committee Chairman Robert W. Goodlatte (R-Va.) said after the briefing that USDA officials admitted "mistakes were made." The committee's ranking Democrat, Rep. Charles W. Stenholm (Tex.), said the improper import permits constituted "a breakdown in the process."

"The secretary was saying one thing, and something different was happening," Stenholm said. "When you have a policy that isn't being carried out, you have a problem."

The agent that causes mad cow disease can be transmitted to humans but has done so rarely. The brain-wasting disease, formally known as bovine spongiform encephalopathy (BSE), has killed about 150 people, mostly in Europe.

Since mad cow disease was found in Canadian cattle, the USDA has been under strong pressure from Canada and large U.S. beef operations with facilities in Canada to relax the ban on Canadian beef products.

There was some dispute yesterday about how much processed beef entered from Canada. Census Bureau import statistics analyzed by a cattlemen's group critical of the USDA showed that 33 million pounds of processed beef were imported between September and February.

But the USDA said its investigation showed that only 7.3 million pounds had come improperly from Canada between September and April. Included in that count were 2.6 million pounds of partially cooked hamburger patties, raw ground beef and frozen dinners, and 2.5 million pounds of hot dogs and cooked sausages.

During a teleconference, USDA officials said that Veneman knew nothing about the processed beef imports and that the permits were approved by lower-level officials.

"The secretary was not aware that [the Animal and Plant Health Inspection Service] was issuing permits for processed products," USDA spokeswoman Alisa Harrison said yesterday. "While following proper food safety procedures . . . APHIS failed to obtain approval for their actions from appropriate USDA policy and legal representatives."

The statement that Veneman did not know of the improper imports was received with skepticism by the man who uncovered the shipments of banned Canadian beef, Bill Bullard, CEO of the Ranchers Cattlemen Action Legal Fund, which represents small cattle growers.

"I can't believe the secretary didn't know what was going on," he said. "This is among the highest- profile issues in her agency, and it's beyond belief that she would not be fully aware of every step the agency is taking in this area."

He also took issue with USDA statements that the imports posed no additional risk to the public. "The rules were in effect because of the scientific assessment that ground and processed beef posed a greater risk of carrying the mad cow agent," he said. "That means USDA put the American public and cattle herd at unnecessary risk."

The Agriculture Department began issuing the permits to import Canadian processed beef soon after Veneman announced a relaxation of the beef ban in August -- a change that allowed boneless beef, but not processed beef, to be imported.

At the time, top USDA officials said that a formal rulemaking process, with an opportunity for public debate, would determine when and whether live Canadian cattle and higher-risk beef products should be allowed back into the United States.

By September, however, the inspection service was issuing permits for processed beef and it was coming into the United States, mostly through Buffalo. The permits became publicly known last month as the result of a lawsuit filed by the cattlemen's legal fund.

In the teleconference yesterday, DeHaven also said an expansion of the agency's mad cow detection program was on schedule to go into effect on June 1. Under that program, the USDA plans to test more than 200,000 animals for mad cow disease over the next 18 months.

DeHaven said that with the expanded surveillance, the agency expects to see periodic false-positive findings, which he said will be publicly reported. "I think it's also important to acknowledge that in fact it is possible that we will find an additional BSE-positive cow," he said.