WASHINGTON (AFP) -- The Bush administration concealed at least one "major" intelligence operation from Congress in possible violation of the law and briefed lawmakers only after they had learned about it from independent sources, a ranking Congressman said Sunday.

The charge by Republican Representative Peter Hoekstra, chairman of the House Intelligence Committee, calls into question repeated assurances by President George W. Bush and his top aides that they strictly comply with disclosure requirements.

They also follow allegations the administration may have acted illegally by authorizing wiretaps on American citizens in the wake of the September 11, 2001, terrorist attacks without requisite court warrants.

Hoekstra, who appeared on the "Fox News Sunday" television program, made clear the operation in question was different from the wiretapping controversy or the covert monitoring of international financial transactions that the administration has been defending in recent weeks.

"There are lots of programs going on in the intelligence community," the committee chairman said.

"But in this case, there was at least one major, what I consider significant, activity that we had not been briefed on."

U.S. law requires that the intelligence panels of both the Senate and the House of Representatives be informed of the government's intelligence activities.

According to Hoekstra, he and other members of his committee learned about this and other undisclosed operations from whistleblowers, or concerned government employees who alerted Congress to what they saw as breaches of the law.

The disclosure prompted him last May to fire off an angry letter to Bush to remind his of his legal responsibility to "fully and currently" inform Congress of intelligence operations.

"If these allegations are true, they may represent a breach of responsibility by the administration, a violation of law, and, just as importantly, a direct affront to me and the members of this committee who have ardently supported efforts to collect information on our enemies," Hoekstra wrote. He said Sunday the administration had since complied with his demand, but added he was taking the situation "very, very seriously."

"I want to set the standard there that it is not optional for this president or any president or people in the executive community not to keep the intelligence committees fully informed of what they are doing," Hoekstra told Fox.

Remarkably, Hoekstra has been a fervent supporter Bush in both the warrantless wiretap and financial monitoring controversies.

The monitoring that came to light last month involved millions of records held by the Belgium-based Society for Worldwide Interbank Financial Telecommunication (SWIFT), an international cooperative that serves as a clearing house for the transactions. Its database, officials say, has provided valuable information about ties between suspected terrorists and groups financing them.

But while key members of Congress agreed the financial monitoring may have been legal, they are far from certain in the case of warrantless wiretaps that has been making headlines since last December.

The Foreign Intelligence Surveillance Act of 1978 mandates that such surveillance be authorized by a special secret court. The White House sought to play down the news controversy, with spokesman Alex Conant telling the AFP the administration continued "to work closely" with Chairman Hoekstra "and other congressional leaders on foreign and national security issues."