Treasury Secretary John Snow on Friday said a program tracking millions of financial transactions was not invasion of privacy of Americans but "government at its best" and vital to the war on terrorism.

Snow told a news conference the program, run by the CIA and overseen by the Treasury Department, was "responsible government, it's effective government, it's government that works."

"It's entirely consistent with democratic values, with our best legal traditions," Snow said.

The once-secret program, which has been going on since shortly after the Sept. 11, 2001, terror attacks, has drawn protests from Democrats in Congress, who said it raises concerns about intrusions on privacy and who saw it as the latest step in an aggressive Bush administration expansion of executive-branch powers.

Snow defended the newly disclosed program, saying it was an effective tool in tracking the financial operations of terrorists.

"By following the money we've been able to locate operatives, we've been able to locate their financiers, we've been able to chart the terrorist networks and we've been able to bring the terrorists to justice," he said.

"If people are sending money to help Al Qaeda, we want to know about it," Snow said.

He said Congress had been briefed on the program.

At the White House, presidential spokesman Tony Snow said the focus had been shutting off terrorist financing. "It's a good thing to shut off the spigot, the financial spigot," he said. "It does seem to be working."

In the weeks following the Sept. 11 attacks, Treasury officials obtained access to an extensive international financial data base — the Society for Worldwide Interbank Financial Telecommunication, or Swift.

The cooperative, based in Belgium, handles financial message traffic from thousands of financial institutions in more than 200 countries

"It's important to understand that very significant protocols and safeguards have been put in pace in a cooperative way between Swift and the Treasury Department," Snow said.

He said that access to the data that had been collected was limited to people with appropriate security clearances.

Snow declined to give specific examples of where the program had been successful in shutting off terrorist financing, but said that he had assured himself that it was working.

The administration used broad subpoena powers to get access to the data.

In a statement, Swift said it had negotiated with the U.S. Treasury "over the scope and oversight of the subpoenas."

Disclosure of the program comes on the heels of intense controversy over President Bush's ordering of National Security Agency surveillance of telephone calls and e-mails of private citizens.

Rep. Ed Markey, D-Mass. , co-chairman of the Congressional Privacy Caucus, said Friday there were disturbing similarities between the two programs.

"Like the domestic surveillance program exposed last December, the Bush administration's efforts to tap into the financial records of thousands of Americans appear to rely on justifications concocted without regard to current law," Markey said in a statement.

However, Republicans defended the effort. Senate Majority Leader Bill Frist of Tennessee had been briefed on the program and had "full confidence in the effectiveness of, and the legal authority for, this vital anti-terrorism tool," said Frist spokeswoman Amy Call.

Snow insisted that the effort was not "data mining or trolling through the private financial records of Americans" nor "a fishing expedition."

"This terrorist tracking program...is really government at its best," the Treasury secretary said.

Stuart Levey, Treasury's undersecretary for terrorism and financial intelligence, called the program a "legal and proper use of our authorities."

Asked how many transaction searches had been made under the program, Levey told reporters there were "at least tens of thousands, maybe hundreds of thousands."

He said individual ATM deposits and withdrawals and sending checks within the United States were not among those transactions monitored.

The consulting firm of Booz Allen Hamilton was retained to audit and review the U.S. activities in the program, Levey said. "They have found consistently the government is not abusing this data," Levey said.

Under the program, U.S. counterterrorism analysts could query Swift to look for information on activities by suspected terrorists as part of specific terrorism investigations, a Treasury official said. They would do so by plugging in a name or names, the official said.

Swift handles financial message traffic from 7,800 financial institutions in more than 200 countries.

The service, which routes more than 11 million messages each day, mostly captures information on wire transfers and other methods of moving money in and out of the United States. It doesn't execute these money transfers. The service generally doesn't detect private, individual transactions in the United States, such as withdrawals from an ATM or bank deposits. It is aimed mostly at international transfers.

The existence of the program was first reported Thursday night on the Web sites of The New York Times, the Los Angeles Times and The Wall Street Journal.

The decision to publish was "a tough call; it was not a decision made lightly," said Doyle McManus, the Los Angeles Times' Washington bureau chief.

Treasury Department officials spent 90 minutes Thursday meeting with the newspaper's reporters, stressing the legality of the program and urging the paper to not publish a story on the program, McManus said in a telephone interview.

The New York Times and Los Angeles Times quoted their editors as defending their decision to publish the financial data tracking effort despite being asked by the administration to withhold publication.

Bill Keller, The New York Times' executive editor, said it considered the administration's arguments but in the end decided to publish. "We remain convinced that the administration's extraordinary access to this vast repository of international financial data, however carefully targeted use it may be, is a matter of public interest."

Dean Baquet, editor of the Los Angeles Times, said: "We weighed the government's arguments carefully, but in the end we determined that it was in the public interest to publish information about the extraordinary reach of this program."