SBC, the No. 2 regional phone company and a major local telecommunications service provider in the Midwest and West, has received about 300 such subpoenas and has refused to answer any of them. It has stuck to that position even though Verizon, the biggest local phone company which has most of its customers along the East Coast lost a major lawsuit this year against the recording industry.

The contrast between SBC’s stance and that of its peers illustrates how Internet providers have been caught in the middle of the music industry’s pursuit of individual music swappers. Their range of responses underscores the complexities of the legal landscape in this new area of law, the mounting tensions between copyright enforcement and privacy, and the limits of technology in finding cyberspace pirates.

In the Verizon case, a federal judge in Washington ruled that the Digital Millennium Copyright Act of 1998 required the company to reveal the identities of its customers even though the industry’s subpoenas had not been individually reviewed by a judge. Oral arguments in Verizon’s appeal are to be heard today by a federal court in Washington.

Most big Internet providers say that the original decision in the Verizon case essentially validated the subpoenas that the recording industry sent to other companies. SBC, however, has sued the recording industry group in California.

“We are going to challenge every single one of these that they file until we are told that our position is wrong as a matter of law,” James D. Ellis, general counsel for SBC, said yesterday in a telephone interview.

Ever since the Telecommunications Act of 1996 remade the communications industry, SBC has been considered by far the most legally aggressive of the nation’s major communications companies. Mr. Ellis is scheduled to testify tomorrow about the copyright subpoenas before the Senate Commerce Committee. With about three million high-speed data customers, SBC is the nation’s No. 1 provider of broadband Internet access using digital subscriber line technology.

“Clearly, there are serious legal issues here, but there are also these public policy privacy issues,” Mr. Ellis said. “We have unlisted numbers in this industry, and we’ve got a long heritage in which we have always taken a harsh and hard rule on protecting the privacy of our customers’ information.”

Recording industry officials see SBC’s stance not as a matter of principle over privacy but as a matter of dollars from downloading. They assert that SBC is not concerned about copyright protection because the company uses the lure of music piracy to attract high-speed Internet customers.

A record industry official pointed to a past print advertisement from SBC’s Pacific Bell unit that read, in part: “Download all the music you like. And all the music you sort of, kind of, maybe even a little bit like. Go MP3 crazy. Try new music. Build a song library. Whatever.”

“Sure beats going to the record store,” the advertisement concluded.

A spokesman for the record industry group said the ad had appeared in The Los Angeles Times as recently as January 2002.

Matthew J. Oppenheim, the trade group’s senior vice president for business and legal affairs, said the ad was important because it suggested a strong motive for SBC’s position. “SBC believes that free music drives its business,” he said. “That’s the only explanation for why they would relitigate issues that have been resolved.”

An SBC spokesman, Selim Bingol, said the advertisement was irrelevant. “It’s ludicrous to suggest that an ad that has not appeared for many months has anything to do with today’s debate,” he said. “We are opposing these subpoenas because under the R.I.A.A.’s interpretation, they are a threat to consumer privacy and safety.”

The wave of subpoenas that led to last week’s lawsuits began about 10 weeks after the judge in the Verizon case issued his final ruling in April. On July 7, the Monday after the Independence Day weekend, lawyers at Internet providers returned to their offices to find a blizzard of legal requests from the recording association. Comcast, the nation’s leading provider of high-speed Internet access to homes, which it supplies through its cable system, received more than 100 subpoenas in the first two days after the holiday.

“It really was a fire drill,” said Gerard J. Lewis, Comcast’s chief privacy officer. At Comcast and other companies, the first subpoenas were dated July 3, the last day before the holiday weekend, and they required the companies to provide the information within seven days. That meant that Internet providers that thought the subpoenas were legal had only two or three days to comply.

Now, according to lawyers at several major Internet companies, the recording industry has agreed to a looser schedule: 10 business days from when the Internet provider receives the subpoena.

The digital copyright law does not require anyone to notify consumers that their personal information has been subpoenaed. It appears, however, that most major Internet providers including Comcast, Time Warner Cable and Verizon made an effort to send letters to many customers who were the subjects of subpoenas, notifying them that unless the customer signaled legal action, the information would be provided to the recording industry.

According to executives at several major Internet providers, only the barest minimum of customers took any steps to block the disclosure of their information. Of the 261 individuals sued by the industry so far, however, a number have said they never received any notice from their Internet provider.

Tracking down the numeric Internet protocol, or I.P., address employed by any given user of a file-sharing network is relatively easy. In essence, the industry focused on users who appeared to be making large numbers of music files available to others on file-swapping networks like KaZaA and Morpheus. Industry investigators noted the I.P. address of the user and the exact time at which the user was making files available.

The recording investigators could then determine which Internet provider assigned the specific I.P. address. The subpoenas included both the I.P. address and the time so that the Internet provider could see which of its customers was using that address at that particular moment. With many consumer Internet services, the I.P. address for a user can change every time the computer is turned off and turned back on, so the exact time is a critical tool for matching I.P. addresses and users.

The length of time that Internet providers maintain logs of users, addresses and times varies. Comcast and Time Warner Cable, for instance, generally keep those logs for only 30 days. That means that if those companies receive a copyright subpoena with an I.P. address and time more than a month old, they may be unable to answer the request.

Verizon, by contrast, generally keeps its I.P. logs indefinitely.

“Verizon keeps that sort of information for traffic management and to help law enforcement,” said Sarah Deutsch, a Verizon vice president and associate general counsel.

Mr. Oppenheim from the recording industry association said he was generally pleased with the level of cooperation his organization has received. Nonetheless, executives at several Internet providers that are cooperating with the association expressed privately some discomfort with the process.

“We fully understand that copyright protection is a legitimate goal,” said one executive at a major Internet provider. “That being said, it doesn’t seem like the consumers’ privacy interest is really being balanced out here in this process.”