The operation, which agents described as the largest anti-steroid action by law enforcement ever, involved cooperation among 10 nations and involved raids and arrests in Mexico, Canada, Australia, Belgium, Denmark, Germany, Sweden and Thailand, U.S. officials said.

Under pressure from Olympic and world anti-doping officials to address China's reputation as the main global supplier of illicit performance-enhancing drugs with the 2008 Summer Games in Beijing just 11 months away, Chinese authorities cooperated with the probe, DEA officials said. The Chinese agreed to accept information packets from U.S. and international law enforcement agencies in the coming weeks to address further the problem within their borders, the officials said.

News conferences to announce details of the busts were scheduled for Sunday in New York, San Diego, Houston, Kansas City, Mo., and Providence, R.I. While some of the individual busts over the last 18 months have been reported, the scope of the action has not been made public until now. Officials withheld announcements on the various raids to ensure the safety of agents as the last round of raids took place this weekend, officials said.

The action targeted underground labs that peddled steroids, human growth hormone and other drugs to customers through Web sites and message boards. It is not yet known whether high-profile Olympic or professional athletes were clients of any of the labs, DEA spokesman Dan Simmons said.

Officials from major sport anti-doping bodies including the World Anti-Doping Agency and U.S. Anti-Doping Agency assisted throughout, offering expertise and support, Simmons said. WADA Chairman Dick Pound is scheduled to arrive in Beijing on Tuesday, where he is expected to follow up on issues surrounding the manufacture and supply of steroids and other drugs from China, which he raised during meetings last fall with Chinese Olympic and government officials as among threats to the legitimacy of competition at the Olympics next August.

China already has taken action against at least one of its companies, Simmons said.

"Chinese authorities were willing partners," he said. "They said they would in fact make efforts to arrest and prosecute violators there in China."

The massive probe could have unusual and unnerving repercussions for the clientele of the labs, as the DEA has begun compiling a database of names of those who ordered or participated in illicit performance-enhancing drug activities through the labs for the use of all law enforcement bodies in the United States, Simmons said.

Simmons declined to elaborate on the intended use or makeup of the database, which he said is being assembled from hundreds of thousands of e-mails and Internet exchanges. He said it would be up to the individual U.S. attorney's offices prosecuting the cases — at least five, including the southern districts of New York and California, are involved — to decide how to handle information that arises regarding well-known athletes.

He added that the probe has no connection to the Signature Pharmacy investigation out of Albany, N.Y., a probe into illegal prescriptions of performance-enhancing and other drugs that has implicated a number of major league baseball and NFL players, coaches and doctors.

Since its inception early in 2006, what has been called Operation Raw Deal resulted in the seizure of at least 242 kilograms of raw steroid powder from China and 11.4 million dosage units of steroids or other chemicals, along with $6.5 million in cash, 25 vehicles and 71 weapons, according to Rusty Payne, a spokesman at DEA headquarters in Alexandria, Va. Fifty-six labs have been seized.

Approximately 70 percent of the enforcement action has occurred since Thursday, Payne said. Specific details of the actions taken overseas were not available as of Sunday, but China was considered the source of the "vast majority" of the illicit drugs, Simmons said.

U.S. law enforcement considered indicting the Chinese companies that supplied the illicit drugs, but decided that a partnership with the Chinese authorities would be more productive, Simmons said. Several agents flew to China this February to discuss the investigation.

The probe targeted raw material manufacturers and suppliers primarily in China and underground drug laboratories in the United States, Canada and Mexico.

It further looked at U.S.-based Web sites that market "conversion kits" that allow for the at-home processing of steroid powders, as well as Internet bodybuilding discussion boards that facilitate and instruct on the illegal use and production of performance-enhancing drugs.

"Operation Raw Deal uncovered a clandestine web of international drug dealers who lurk on the Internet for young adults craving the artificial advantage of anabolic steroids," DEA Administrator Karen P. Tandy said in a statement. "Today we reveal the truth behind the underground steroid market: dangerous drugs cooked up all too often in filthy conditions with no regard to safety, giving Americans who purchase them the ultimate raw deal."

Recent raids turned up anabolic steroids, human growth hormone, insulin growth factor and other drugs and chemicals including ketamine, fentanyl, ephedrine, pseudoephedrine, and GHB, Payne said.

The operation grew out of a massive bust in Mexico in 2005 known as Gear Grinder, which took down eight Mexican steroid producers credited with supplying more than 80 percent of the illicit steroids in the United States. That bust, Simmons said, pushed virtually all of the remaining U.S. steroid business to China.

Simmons said the labs taken down in the various busts showed no adherence to any standards for safety or sanitation, with drugs being mixed in basements or bathtubs before being shipped out to consumers.

Steroids and other performance-enhancing drugs are banned by the Olympic movement and most major sports leagues. Side effects of anabolic steroids, which increase muscle mass, include increased body hair, a deepening of the voice, enlargement of the breasts in men and a shrinking of the testicles.

Human growth hormone, believed to build strength and help muscles recover better from injury, can cause an enlargement of the jaw, forehead and hands and feet.