A year ago, Colleen Rowley, the FBI whistleblower, accused the FBI and the Department of Justice (DOJ) of being too timid and of short-circuiting FBI field investigations of potential terrorist activity with links to Sept. 11.

But as we become more aggressive in fighting terrorism, a careful balance is required. Many Americans are unaware of a so-called secret court known as the Foreign Intelligence Surveillance Court (FISC), which was created in 1978. It is a small court of eleven federal district judges that hears applications from the federal government to use surveillance tools to eavesdrop on foreign-intelligence activity-including both terrorism and clandestine spying-on American soil.

In May, FISC issued an important joint opinion rejecting a request from DOJ's Office of Intelligence Policy and Review for expanded authority. The office wanted to allow law enforcement personnel, including the FBI and DOJ prosecutors, to direct the use of foreign-intelligence methods in investigating terrorists' domestic criminal acts.

Where Rowley saw a timid agency, however, FISC saw an overly aggressive one. The court was unwilling to authorize an expansion of investigative power because, in the court's view, the FBI had, on at least 75 occasions in the 1990s, filed misleading and erroneous declarations with the court.

FISC's decision is now on appeal to the Foreign Intelligence Surveillance Court of Review (comprised of three federal appellate judges), which met for the first time in history last month. The unclassified portion of its decision will be released soon. The court of review should affirm the FISC decision.

The 1978 Foreign Intelligence Surveillance Act (FISA) has a requirement that FBI agents applying for warrants to conduct electronic surveillance certify that the "primary" purpose of the surveillance is to uncover activity of foreign persons or governments. Because the Fourth Amendment does not apply with the same rigor to searches of foreigners, it is easier to get a warrant under the act than under general criminal law standards. The probable-cause standard under the act is much lower than for a wiretap under the domestic surveillance law-Title III of the Omnibus Crime Control and Safe Streets Act of 1968.

Given the potential that law enforcement might systematically substitute the lenient FISA procedures for more stringent Title III procedures, FISC historically has erected a wall between law enforcement investigations and foreign- intelligence investigations. It has interpreted FISA to prohibit law enforcement from directing the initiation or operation of a search under the act. For example, law enforcement agents could not tell the foreign-intelligence agents what sorts of information to seek.

FISC has allowed only limited information sharing between foreign and domestic agencies. Catching crooks has been kept almost wholly separate from catching spies.

Late last year, Congress passed the USA Patriot Act. Now, rather than requiring that the "primary purpose" of a warrant is to uncover foreign-intelligence activity, agents need demonstrate only that uncovering such activity is a "significant" purpose of the warrant. This permits the FBI to have the substantial-and perhaps "primary"-purpose of conducting a criminal law enforcement investigation using foreign-intelligence means.

Responding to the new law, DOJ sought to modify the court's historical understanding of FISA; it wanted increased information-exchange authority and greater ability for criminal prosecutors to control FISA investigations.

FISC gave DOJ half a loaf. It approved greater information sharing, but decided that the change in the purpose requirement of FISA had not changed the prohibition on law enforcement control of a foreign-intelligence investigation. This strikes the right balance.

The public's interest in more effective investigation and prosecution of terrorists is substantial. Few doubt that we need to foster increased coordination between foreign-intelligence officers and domestic criminal law enforcement authorities. Since the 1970s, we have over-reacted to the public's fear of the foreign-intelligence community and erected unreasonably high walls between foreign and domestic organizations.

There is no reason the FBI and the CIA should not share information where concerns overlap. Most terrorist acts also are crimes. Information lawfully obtained during a FISA search that also discloses criminal activity should be shared with law enforcement. Thus, FISC was right to loosen the constraints and allow a greater exchange of information.

But allowing prosecutors and law enforcement agents to start and direct FISA investigations and do so for the principal purpose of collecting criminal evidence would be a process more vulnerable to abuse. So long as one of the people under investigation is a foreign citizen who has a colorable connection to a terrorist organization, the lenient standards of FISA would apply and the more significant restrictions of the Fourth Amendment and Title III might be avoided.

Indeed, to allow criminal investigators to use FISA would read into the change of a single word (from "primary" to "substantial") a larger change in our laws on domestic surveillance. It is most unlikely that Congress intended so drastic a change. Without clear authorization from Congress, FISC was right to maintain the status quo-and its decision should be upheld on appeal.

Paul Rosenzweig is the senior legal research fellow in the Center for Legal and Judicial Studies at the Heritage Foundation and adjunct professor of law at George Mason University.