ASHINGTON, Jan. 30 — Law enforcement officials across the country will soon have access to a database of 50 million overseas applications for United States visas, including the photographs of 20 million applicants.

The database, which will become one of the largest offering images to local law enforcement, is maintained by the State Department and typically provides personal information like the applicant's home address, date of birth and passport number, and the names of relatives.

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It is a central feature of a computer system linkup, scheduled within the next month, that will tie together the department, intelligence agencies, the F.B.I. and police departments.

The new system will provide 100,000 investigators one source for what the government designates "sensitive but unclassified" information. Officials see it as a breakthrough for law enforcement, saying it will help dismantle the investigative stumbling blocks that were roundly criticized after the Sept. 11 attacks.

At the same time, they acknowledge the legal and policy questions raised by information sharing between intelligence agencies and local law enforcement, and critics have cast a wary eye as well at the visa database.

One other effect of the new system is that for the first time, the Federal Bureau of Investigation and other agencies linked by it will be able to send one another encrypted e-mail. Previously, security concerns about the open Internet often caused sensitive information to be faxed, mailed or sent by courier.

The changes come as the F.B.I. continues working to upgrade its entire computer system, which is so antiquated and compartmentalized that it cannot perform full searches of investigative files. The bureau's director, Robert S. Mueller III, has said that while the technology easily allows for single-word searches, for example for "flight" or "school," it is very hard to search for a phrase, for example "flight school."

For all the ambitious technological proposals being debated in the wake of the 2001 terror attacks, the new unified system was cobbled from existing networks and has required little new spending. "These are the networks that people are already using," said Roseanne Hynes, a member of the Defense Department's domestic security task force. "It doesn't change jobs or add overhead."

A primary feature of the system is the State Department's enormous visa database, whose seven terabytes give it a capacity equivalent to that of five million floppy disks. Until now, that database has been shared only with immigration officials.

"There is a potential source of information that isn't available elsewhere," said M. Miles Matthew, a senior Justice Department official who works with an interagency drug intelligence group. "It's not just useful for terrorism. It's drug trafficking, money laundering, a variety of frauds, not to mention domestic crimes."

Local law enforcement agencies seeking photographs have typically had immediate access only to their own database of booking photos. But to get photos of people not previously charged or arrested, an investigator would make a request to a motor vehicle department or the State Department.

So officials emphasize that the State Department database is not making any information newly available to law enforcement, simply making such information easier to acquire. But that increasing ease of accessibility raises some concern from civil liberties groups.

"The availability of this information will change police conduct," said Marc Rotenberg, executive director of the Electronic Privacy Information Center, which has advocated more Congressional oversight of domestic security operations. "You are more likely to stop someone if you have the ability to query a database."

Or, as Mr. Rotenberg also put it: "The data chases applications."

Critics also point to what they call the unwelcome precedent of foreign-intelligence sharing with local law enforcement, even if the intelligence community's initial contribution to the new system may seem somewhat innocuous. That component is the Open Source Information System, a portal where 14 agencies pool unclassified information. Such material in the new system will includes text articles from foreign periodicals and broadcasts, technical reports and maps.

Two domestic law enforcement networks are also being tied in: Law Enforcement Online, a seven-year-old system established by the F.B.I., and the Regional Information Sharing Systems, six geographically defined computer networks that help local law enforcement agencies collaborate on regional crime issues like drug trafficking and gangs.

Becoming part of a collaborative computer network is unusual for the F.B.I., which has been criticized for its insular nature and technological sluggishness. As some agents joke, the bureau "likes to have yesterday's technology tomorrow." Many agents do not have direct access from their desks to the Internet, because of security concerns. Instead, some field offices have separate areas that agents refer to as "cybercafes," where they can log on to the Internet.

The bureau is now engaged in a multibillion-dollar effort to upgrade its computer system. A recent report by the Justice Department's inspector general cited mismanagement of the project, though Director Mueller gave reporters a sunny assessment today, saying among other things that parts of the upgrade would go online in March as scheduled.

As for the new interagency system, other large security and law enforcement computer networks are scheduled for integration with it within the next year.

These include an unclassified part of the Defense Department computer network, as well as the National Law Enforcement Telecommunication System, which is used to disseminate criminal justice information nationwide.