In the first public accounting of its kind, cellphone carriers reported that they responded to a daunting 1.3 million demands for subscriber data last year from law enforcement agencies seeking text messages, caller locations and other information in the course of investigations.

The data, which comes in response to a congressional inquiry, documents an explosion in cellphone surveillance in the last five years, with the wireless carriers turning over records thousands of times a day in response to police emergencies, court orders, law enforcement subpoenas and other requests.

The cell carriers’ reports also reveal a sometimes uneasy partnership with law enforcement agencies, with the carriers frequently rejecting demands they considered legally questionable or unjustified. Carriers even referred some inappropriate requests to the F.B.I.

The statistics represent the first time data has been collected nationally on the frequency of cell surveillance by law enforcement. The volume of the requests reported by the carriers — which most likely involve several million subscribers — even surprised some officials who have closely followed the growth of cell surveillance.

“I never expected it to be this massive,” said Representative Ed Markey, the Massachusetts Democrat who requested the data from nine carriers, including Sprint, AT&T, Verizon and T-Mobile, in response to an article in April in The New York Times on law enforcement’s expanded use of cell tracking. Mr. Markey, who is co-chairman of the Bipartisan Congressional Privacy Caucus, made the carriers’ responses available to The Times.

While the cell companies did not break down the types of law enforcement agencies collecting the data, they made clear that the widened cell surveillance cuts across all levels of government — from run-of-the-mill street crimes handled by local police departments to financial crimes and intelligence investigations at the state and federal levels.

AT&T alone now responds to 230 emergency requests a day nationwide — triple the number it fielded in 2007, the company told Mr. Markey. Law enforcement requests of all kinds have been rising quickly among the other carriers as well, with annual increases of 12 percent to 16 percent in the last five years. Sprint led the way last year, reporting more than 500,000 law enforcement requests for data.

With the rapid expansion of cell surveillance have come rising concerns — even among the carriers — about what legal safeguards are in place to balance law enforcement agencies’ needs for quick information against the privacy rights of consumers.

Legal conflicts between those competing needs have flared before, but usually on national security matters. In 2006, phone companies that cooperated in the Bush administration’s secret program of eavesdropping on suspicious international communications without court warrants were sued, and ultimately were given immunity by the courts. The next year, the F.B.I. was widely criticized for improperly using emergency letters to the phone companies to gather records on thousands of phone numbers in counterterrorism investigations that did not involve emergencies.

Under federal law, the carriers said they generally require a search warrant, court order or formal subpoena to release information about a subscriber. But in cases that law enforcement officials deem an emergency, a less formal request is often enough. Moreover, rapid technological changes in mobile phones have blurred the lines on what is legally required to get data — particularly the use of GPS systems to identify the location of a cellphone.

As cell surveillance becomes a seemingly routine part of police work, Mr. Markey said in an interview that he worries that “digital dragnets” threaten to compromise the privacy of many customers. “There’s a real danger we’ve already crossed the line,” he said.

Mr. Markey and other Democrats are considering legislation that they say would more clearly draw the line between giving the authorities the technological tools they need and protecting the privacy of the public. With the rising prevalence of cellphones, officials at all levels of law enforcement — local police chiefs, state troopers, federal agents, and others — say cell tracking represents a powerful tool to find suspects, follow leads, identify associates and cull information on a wide range of crimes.

“At every crime scene, there’s some type of mobile device,” said Peter Modafferi, chief of detectives for the Rockland County district attorney’s office, who also works on investigative policies and operations with the International Association of Chiefs of Police. The need for police to exploit that technology “has grown tremendously, and it’s absolutely vital,” he said in an interview.