The Department of Homeland Security wants a private company to provide a national license-plate tracking system that would give the agency access to vast amounts of information from commercial and law enforcement tag readers, according to a government proposal that does not specify what privacy safeguards would be put in place.

The national license-plate recognition database, which would draw data from readers that scan the tags of every vehicle crossing their paths, would help catch fugitive illegal immigrants, according to a DHS solicitation. But the database could easily contain more than 1 billion records and could be shared with other law enforcement agencies, raising concerns that the movements of ordinary citizens who are under no criminal suspicion could be scrutinized.

A spokeswoman for DHS’s Immigration and Customs Enforcement agency (ICE) stressed that the database “could only be accessed in conjunction with ongoing criminal investigations or to locate wanted individuals.”

The database would enhance agents’ and officers’ ability to locate suspects who could pose a threat to public safety and would reduce the time required to conduct surveillance, ICE spokeswoman Gillian Christensen said.

“It is important to note that this database would be run by a commercial enterprise, and the data would be collected and stored by the commercial enterprise, not the government,” she said.

But civil liberties groups are not assuaged. “Ultimately, you’re creating a national database of location information,” said Jennifer Lynch, a staff attorney with the Electronic Frontier Foundation. “When all that data is compiled and aggregated, you can track somebody as they’re going through their life.”

ICE issued a notice last week seeking bids from companies to compile the database from a variety of sources, including law ­enforcement agencies and car-

repossession services.

Agents would be able to use a smartphone to snap pictures of license plates that could be compared against a “hot list” of plates in the database. They would have 24-hour, seven-day-a-week access, according to the solicitation, which was first noted last week by bloggers.

“The government would prefer a close-up of the plate and a zoomed-out image of the vehicle,” the document said. The images would go in a case file report that would include maps and registration information, as well as the car’s make and model.

The agency said the length of time the data is retained would be up to the winning vendor. Vigilant Solutions, for instance, one of the leading providers of tag-reader data, keeps its records indefinitely.

Nationwide, local police as well as commercial companies are gathering license-plate data using various means. One common method involves drivers for repossession companies methodically driving up and down streets with cameras mounted on their cars snapping photos of vehicles. Some police forces have cameras mounted on patrol cars. Other images may be retrieved from border crossings, interstate highway on-ramps and toll plazas.

“The technology in use today basically replaces an old analog function — your eyeballs,” said Chris Metaxas, chief executive of DRN, a subsidiary of Vigilant Solutions, which since its founding in 2009 has amassed one of the largest warehouses of license-plate data in the country. “It’s the same thing as a guy holding his head out the window, looking down the block, and writing license-plate numbers down and comparing them against a list. The technology just makes things better and more productive.”

Vigilant’s National Vehicle Location Service (NLVS), which holds more than 1.8 billion records, is offered to law enforcement agencies across the country. ICE has tested the service at no charge, according to documents obtained by the American Civil Liberties Union under a Freedom of Information Act request.

“The results have been excellent, accounting for approximately 100 arrests in a 6-month time period,” said one of the DHS documents obtained by the ACLU, dated Jan. 9, 2012. “Some of the cases that resulted in arrests were formerly thought to be cold cases.”

In one 2010 case, a mother and two adult children began using a post office box after they were ordered to be deported, according to the document. Three vehicles were registered to a house the family owned, but the house was rented out and the cars were never parked there. Two of the three vehicles were found, at different addresses, using the NVLS, the document said.

Some questions about ICE’s plan remain open. The agency could not say how long the data would be stored, which other law enforcement agencies would have access to it and what constitutes an “investigative lead” to allow database querying.

The FBI since 2004 has partnered with nearly every state and dozens of local agencies to compare license plates against the National Crime Information Center database and said the data have helped locate more than 800 wanted people. The bureau has been working on a privacy impact assessment of its license-plate reader program since early 2012, but no assessment has been made public, said Jeramie Scott, national security counsel for the Electronic Privacy Information Center, an advocacy group.

Customs and Border Protection, another DHS agency, and the Drug Enforcement Administration, which is part of the Justice Department, also have deployed cameras along the country’s borders.

But DHS’s effort appears to be the first time a federal law enforcement agency is seeking such extensive access to a broad repository of data capturing the movements and images of American motorists from metropolitan ­areas.

The ACLU said it has no objection to law enforcement officials checking license plates to see whether they’re associated with a stolen car or a felon evading arrest. But the government’s access to vast amounts of data on ordinary, law-abiding citizens raises concerns about potential abuse, advocates said. “This is yet another example of the government’s appetite for tools of mass surveillance,” said Catherine Crump, staff attorney for the ACLU, which issued a report last year that criticized the growing use of the devices without adequate privacy protections.

The DHS effort arises as states are confronting policy choices about the use of license-plate readers. Laws vary across jurisdictions on how long data can be stored and who may have access. Some delete the data after 48 hours. Others keep it indefinitely. About 20 states have passed or proposed legislation that would restrict the use of such readers or the storage of the data. Utah has a law prohibiting commercial companies from using automated high-speed cameras to photograph license plates. Vigilant has filed a First Amendment lawsuit to overturn the ban.

This month, the Virginia General Assembly shelved for a year legislation that would have banned local police from collecting data from license-plate readers. The state attorney general last year declared the collection of such data illegal.

Maryland is considering legislation that would ban non-

government deployment of tag readers and regulate their use by government agencies.

Only a handful of companies gather license-plate data on a national scale, industry officials said. But DRN and Vigilant are the dominant players in the industry, with DRN capturing an estimated 70 percent of the commercial market and Vigilant about 90 percent of the law enforcement market, said Jack Bernstein, chief executive of Locator Technologies, another company in that field.

“I know the data is really valuable,” Bernstein said, “and I know the potential for abuse is significant.”