They called him "Deep Throat," the mysterious and anonymous source who helped lead Bob Woodward and Carl Bernstein of The Washington Post to information that ultimately ousted President Richard M. Nixon in the early 1970s scandal we know as Watergate.

That image — earnest reporters laboring for the public good against Nixon's dirty tricks — is deeply ingrained in American journalism lore. However, as reporters three decades later attempt to protect anonymous sources similar to "Deep Throat," they face a new playing field, new political climate and new public attitudes.

No one in 1973 had heard of the Internet, let alone a "blogger." Television news meant three networks, epitomized by the trusted "Uncle Walter" Cronkite. Rush Limbaugh and Fox News were in the unseen future.

Technology, politics and journalism have changed enormously, and the public's right to know — the reason for the First Amendment — is headed for the Supreme Court in the most serious clash between the White House and news media since Nixon's time.

Simultaneously, legislation introduced in Congress with bipartisan support would establish federal protection for anonymous sources. A House hearing on Thursday begins the process, running parallel to court proceedings.

At least 20 reporters have been threatened with prison or heavy fines as the Justice Department, in separate cases, pushes them to reveal confidential sources.

The most prominent of the so-called "reporter shield" cases involves a 2003 case in which an unnamed Bush administration source, attempting to discredit a critic, told conservative columnist Robert Novak that the critic's wife was an undercover CIA agent.

Novak "outed" agent Valerie Plame, prompting other news outlets to follow suit. Blowing an agent's cover can be a federal offense. Only someone with top-security clearance would have known Plame's identity; this was not a low-level deal.

The administration had no choice but to investigate. Not surprisingly, no one from the administration has been indicted. But several reporters were subpoenaed and two, Judith Miller of The New York Times and Matthew Cooper of Time, may go to jail for refusing to reveal sources to whom they had promised anonymity. Their cases are headed to the Supreme Court; lower courts have rejected appeals.

These cases are somewhat unusual because someone in the administration itself revealed secret information to embarrass a critic. The classic shield case involves information leaked by a whistle-blower or insider (think "Deep Throat") to protest official abuses.

Many journalists — myself included — believe Novak should not have carried the administration's water, endangering the career and perhaps the life of an agent for purely political reasons. Novak refuses to discuss his role in the case. The key here is not Novak's judgment, but the reporter's right to make that decision.

The alternative is to allow government to force reporters to serve as an arm of the law, informing on those who seek to use the media to right a wrong or expose corruption.

The public's right to know hinges on media access to data and people, sometimes on a confidential basis. When sources cannot count on a reporter to protect their identity, they may remain silent, depriving the public of important information.

The present climate in Washington is a combination of secrecy and intimidation, and the effect is to dry up sources. Former Attorney General John Ashcroft made it more difficult to obtain data under Freedom of Information Act procedures, which led reporters to rely more heavily on anonymous insider sources. At the same time, he relaxed 30-year-old departmental practices to make it easier for federal prosecutors to subpoena reporters.

State and federal laws differ on disclosure of sources, due to a 1972 Supreme Court ruling. In the tumultuous '60s and '70s, prosecutors often had little luck penetrating the drug, anti-war and Black Power movements. Increasingly, they tried to use reporters as sources. The rapid increase in subpoenas was staggering. From 1960 to 1968, only a dozen subpoenas were served on reporters; from 1970 to 1976, about 500 subpoenas were served, including three that brought the Branzburg v. Hayes ruling in 1972.

Justice Byron White, writing for a 5-4 majority, declared that the public interest in investigating and prosecuting crime prevails against the First Amendment argument for a free flow of information. However, the court left the door open for future interpretation and acknowledged that Congress and state legislatures could adopt protective shields for reporters.

Some 50 shield laws were introduced in Congress in 1973. Reporters pressed for broad protection, but the Nixon Justice Department opposed any shield, with future Supreme Court Justice Antonin Scalia as point man. Congress couldn't find a compromise, then or later.

Despite congressional failure, there appears to be public support for a shield. Gallup polls in the '70s asked: "Suppose a newspaper reporter obtains information for a news article he is writing from a person who asks that his name be withheld. Do you think that the reporter should or should not be required to reveal the name of this man if he is taken to court to testify about the information in his news article?" In 1973, 62 percent supported confidentiality, and by 1978 the margin increased to 68-23.

Support continues. The First Amendment Center in October 2004 found that 72 percent supported the statement, "Journalists should be allowed to keep a news source confidential," a stronger margin than during Watergate.

Another 2004 survey showed nearly 80 percent support the media's role as watchdog of government, but about 40 percent also say the media have too much freedom. This ambivalence about the media's role in society is historic; Americans have never trusted either politicians or journalists, but apparently like using confidential informants as a check on power.

The practice of a reporter refusing to reveal a source dates at least to 1857. A New York Times reporter refused to name sources in a story about congressmen taking bribes, and was held by the House for 19 days before being discharged.

Although state shield laws were passed as early as 1898 (Maryland), the 1972 ruling in Branzburg v. Hayes brought a rash of new state laws. Currently, 31 states have shield laws and in most of the others (including Washington), courts have granted common-law protection to reporters.

Hopes for a federal shield rest on the bipartisan nature of shield-law sponsors. Rep. Mike Pence, R-Ind., chairs the conservative House Republican Study Committee, and Sen. Richard Lugar, R-Ind., is widely respected. Democratic sponsors are Rep. Rick Boucher of Virginia and Sen. Chris Dodd of Connecticut. No administration position has been revealed.

One obstacle facing federal shield supporters in 2005 is expansion of the news universe, primarily through the Internet. The explosion of Web logs (blogs) makes defining "journalist" increasingly complex. An estimated 8 million people have posted blogs on the Internet.

Some bloggers are professional journalists, employed by mainstream media. Others range from scholars to teenagers to ideologues with no news training or ethical guidelines. While their opinions are clearly protected by the First Amendment, protecting material based on confidential sources will be contentious.

Legislation introduced by Pence and Boucher protects publishers, broadcasters, wire services, and their employees, including freelancers, but does not include those publishing solely on the Web. Thus, a blogger employed by a media firm would be protected, but an independent blogger would not.

Confidential sources are, and should be, used sparingly by ethical news people. The stakes can be huge (Watergate), but confidentiality also protects frightened but conscientious underlings in city halls, federal and state regulatory agencies and even private business. Protection of a source can save the life of someone with knowledge of police corruption or save the job of a secretary who knows the boss is on the take.

Subpoenas and the threat of jail are often meant to intimidate investigative reporters and their employers, who face the high cost of defending them in court. Reporters call this a "chilling effect," discouraging tough journalism.

In today's national political climate, there is a vital need for source protection. The White House, Congress and (arguably) the Supreme Court are firmly in the hands of one political party. Bush administration officials are notably "on message" and the president himself rarely holds an open news conference. Recent revelations of journalists paid off with federal funds further emphasize the importance of independent scrutiny.

That scrutiny depends in large measure on reversal of Branzburg, an unlikely prospect, or passage of a federal shield law. Branzburg left room for Congress to shield reporters from punitive federal subpoenas, as most states have done.

Pence stated, "I would humbly offer that if we give people the knowledge, the republic will be saved. The media is the only entity in America that has complete freedom to hold government accountable."

Bipartisan sponsorship of federal shield proposals tells us that members of both parties realize this is not a partisan question, but one of the public's right to know, without fear that the messengers will be threatened with jail.

Floyd J. McKay, professor emeritus of journalism at Western Washington University, is a veteran political reporter and regular contributor to Times opinion pages. E-mail him at floydmckay@yahoo.com