Updated

Sen. Russ Feingold, D-Wis., a sharp critic of President Bush's authorization of the National Security Agency's warrantless electronic eavesdropping program, will have more opportunity to question the president's plan when he takes Sen. Jon Corzine's place on the Senate Intelligence Committee.

The Senate reconvenes on Jan. 18, but the Senate Intelligence Committee has no plans yet on whether to take up the NSA eavesdropping issue. Though no action items have been set, a lot of discussions have taken place, said committee staff director Bill Duhnke.

"What to do, when to do it, who's going to do it [are all under consideration]," he said.

Corzine's seat became vacant when he resigned from the Senate after being elected governor of New Jersey. Feingold's assignment becomes effective when the Senate returns.

Feingold, who received the assignment after Senate Democrats met last month, said he is looking forward to joining the panel where he wants to continue to develop "a more effective and comprehensive approach" to the War on Terror while making sure Congress has adequate oversight of the fight.

"Given the recent revelations made by the president that he directed the National Security Agency to spy on American citizens without a warrant, congressional oversight is especially critical right now. The Intelligence Committee, as well as the Judiciary Committee, on which I also serve, has a central role to play in that effort,” he wrote in a statement to FOXNews.com.

Though the entire membership of the House and Senate intelligence committees has not been briefed on the NSA program — only the chairmen and ranking members and leadership of the two chambers have been given the low-down — as a member of the Senate Intelligence Committee, Feingold will be in a better position to learn more about the NSA program and any legal justification for it.

The Wisconsin Democrat told reporters on Wednesday that he does not believe Bush had any legal basis to authorize the warrantless eavesdropping of individuals on American soil who were suspected to have ties to terrorists and had communicated with people overseas.

"The law is very clear that the president did not have the authority on his own to do this outside of the Foreign Intelligence Surveillance Act," Feingold said, referring to the 1978 law that requires federal agents to get a warrant from a secret court in order to wiretap specific phone numbers.

"I think that if there is a domestic connection that they still have to go through FISA ... What we're not open to is the president deciding on his own that he ought to make up a law because he's frustrated that he can't do whatever he wants. That is unacceptable," Feingold said in the conference call.

Feingold's interpretation of the law is at odds with a number of people in the intelligence community and elsewhere who told FOX News that if the information was obtained overseas and a foreign person was the "target" of the surveillance, that the circumstances would be beyond the purview of the Foreign Intelligence Surveillance Act court, which issues warrants.

"What is happening here is that we are beginning the process of monitoring without knowing the target. That's what makes this different from the approach before," said professor Tim Naftali, Miller Center of Public Affairs at the University of Virginia and has written a book on intelligence called "Blind Spot: The Secret History of American Counterterrorism."

"Before, the NSA was an instrument that was used by the FBI or CIA to target certain people or certain governments, known suspects, if you will. Now it's the other way around. The NSA is going to produce possible suspects for further investigation by the FBI and CIA ... So before there is a warrant of any kind because there is no known individual, the NSA is out there looking for suspicious activity.

"This is a collection program that is spitting out lots and lots and lots of names and ... the size of the program makes following the niceties of FISA apparently inconvenient," Naftali added.

"A significant part of this operation is the National Security Agency using its computing capabilities to search against data coming into it, these foreign to U.S. communications, but maybe without actually intercepting the content, just looking for patterns, running it against criteria that might identify terrorists, etc.," said Bryan Cunningham, former deputy legal counsel for the National Security Council. "And of course, unless you are intercepting the content of the communication, then the need to get a foreign intelligence surveillance warrant is not contemplated, even under the statute."

Asked whether it's unreasonable to seek a FISA warrant when the NSA is data mining phone switches and cutting through thousands of phone calls in a short time, Feingold said he didn't necessarily approve of that method for tracking terror either.

"I did not say that I would want to agree to allow them to do all of that. That's a question that would have to be the subject of appropriate hearings and discussions. And if anybody ever wanted to move in that direction, it would have to involve some very specific safeguards," the three-term senator said.

"I don't know whether or not it's actually possible to do and, if it is possible to do, how you would do it? But you can't simply start doing it on your own without a legal authority," Feingold said.

Data mining will continue to be on the minds of administration officials, however. Already, an unidentified intelligence agency, perhaps the NSA, is continuing research on software designed to help track terrorists that was part of a program killed by Congress.

Terrorist Information Awareness, a Pentagon program that emerged in the year after Sept. 11, 2001, was designed to follow the tracks terrorists would have to lay in advance of an attack, for instance, getting a driver's license or taking flying lessons.

Congress killed the program run by Adm. John Poindexter, a controversial figure from the Reagan administration, but approved continuation of the software research. The technology was to be turned over to the FBI and other law enforcement agencies.

In any case, as a member of the Senate Intelligence Committee, Feingold will be in a better position to make an informed judgment about the activities of the NSA, legal restrictions on executive authority and the technology used to track terror. And as a potential presidential candidate in 2008, that position could help lay the groundwork for demonstrating the type of leader he would be in the War on Terror.

FOX News' Sharon Kehnemui Liss and Jim Angle contributed to this report.