LONDON, JAN. 7 -- Although Anthony Cavendish officially left MI6, the British intelligence service, in 1953, he maintained both friendships and an interest in the agency. One of his friends was Maurice Oldfield, who headed MI6 in the 1970s and repeatedly was rumored to be a practicing homosexual.

When stories about Oldfield, who died in 1981, began to circulate again several years ago, Cavendish, according to his own account, decided to say something in his friend's behalf. He wrote a book of memoirs describing his own career, but centering on a special tribute to Oldfield. Although he offered MI6 the opportunity to review it, the agency reportedly declined.

Unable to find a publisher, Cavendish printed 500 copies of the slim volume himself. Last month, he mailed them as Christmas cards.

Thus began the latest skirmish in the British government's ongoing war to protect what it sees as its legitimate secrets. In the last two weeks, it has obtained court orders barring three newspapers from publishing information from the book, on grounds that its mere existence was a breach of Cavendish's lifelong obligation to the state of confidentiality.

A fourth newspaper, the Glasgow Herald, ran extensive excerpts from the memoirs this morning, virtually daring the government to come and get it. The paper acknowledged in an editorial that the largely unsensational contents of the book, much of which has been published outside Britain, might well be of "only passing newsworthiness" and of "no great historical value."

But the government, the Herald said, had made the book interesting by going to such lengths to suppress it.

The Herald's editors received notice tonight that the government would see them in court on Friday morning. Even though it was not a party to the original injunction, the government contends, the Herald was bound by its terms.

Prime Minister Margaret Thatcher sometimes seems to be running out of fingers to plug the leaks springing in the sturdy and all-encompassing dike of secrecy she has sought to construct.

Her government is involved in at least a dozen court cases against the media, including actions against seven newspapers to prevent publication of information about "Spycatcher," the internationally best-selling memoirs of retired counterintelligence agent Peter Wright that are still banned in Britain.

Next week, it faces what is certain to be an angry parliamentary debate over secrecy laws.

Critics charge that the government has pressed its pursuit of bogus national security cases by invoking a number of laws that were never intended for use in such matters.

Under Thatcher, the Police and Criminal Evidence Act has been used to enter newsrooms and reporters' homes for unlimited search-and-seizure expeditions. The government has argued successfully before High Court judges in the "Spycatcher" cases that injunctions won against any individual newspaper legally bind every other paper -- the same argument to be used against the Herald in court Friday.

Confidentiality law, most often used to prevent the leak of corporate and technologically competitive information in private industry, has been invoked to prevent media publication of material disclosed by public officials without authorization.

"The way in which this government's obsession with secrecy is amounting to a campaign against press freedom, and an abuse of the legal system, is becoming a national scandal," said Magnus Linklater, editor of The Scotsman, one of the three newspapers directly enjoined from publishing reports of the Cavendish book.

What the government has not invoked in secrecy cases over the past several years, according to the public prosecutions office, is the Official Secrets Act, the 1911 law that makes it a crime for government employees to disclose information and for newspapers to print it.

The last case involving national security in which the act was invoked was the 1985 trial of Clive Ponting, a senior Defense Ministry official charged with leaking information about the British sinking of the Argentine warship Belgrano during the Falklands war.

The Ponting case was the most sensational in a torrent of leaks that plagued Thatcher in the early 1980s, and her government fought it with a vengeance. The judge instructed the jury that Ponting's defense -- that the government had misled Parliament about the incident and that he therefore was acting in the public interest -- was inadmissible. But the jury overruled the judge, and found Ponting innocent.

Since then, all of the cases the government has fought against the media on various other grounds have been heard before an individual judge or panel of jurists. The government, an editorial in The Guardian charged recently, "is now scared of prosecuting directly, because juries think the secrecy laws are ridiculous and therefore throw out the charges."

But in the face of widespread ridicule over the "Spycatcher" situation, Thatcher has argued repeatedly that the confidentiality claim is a valid one. Allowing any current or former British intelligence official to write about his time on the job, she has contended, even if he only publishes official luncheon menus, would "open the floodgates" to abuse that would ultimately damage national security.

Those who insist on allowing publication of such material, no matter what the circumstances, Thatcher has said, must only be interested in providing information to the enemy.

It is unclear whether the British public shares the outrage of the media and civil libertarians over Thatcher's tactics. Richard Shepherd, one of a sturdy handful of Conservative backbenchers in Parliament who have made their own displeasure known, said he doubted it.

"We are a loyal and homogenous nation; a diffident and deferential society," said Shepherd, a right-winger on many subjects but a self-described "libertarian" on public information issues. "To say this kind of thing erodes freedom is not a proposition supportable to most Britons in ordinary daily life."

Whether the public cares or not, the issue is due to be aired next week, when Parliament will hold its first direct debate in many years on the Official Secrets Act. The occasion is the second reading of a bill that Shepherd, not his party, has introduced, to revise the act's all-encompassing Section Two.

There is little disagreement, even from Thatcher, that Section Two is "laughable and unuseable," according to a spokesman for the Home Office. It makes it a crime for any government employee, in any capacity, to disclose any information whatsoever, for any reason, without authorization.

Technically, the law could be used not only to protect national security information, but for anything from the minutes of public meetings to the test results of students in public schools. Critics charge it can also be used to discourage legitimate public and press inquiry and to frighten officials who want to uncover government abuses.

In 1979, a government effort to revise Section Two failed when Parliament found the proposed new law too restrictive. Since then, while insisting that the law should be changed, the government has made no attempt to do so.

It has sharply opposed Shepherd's bill, however, arguing that such an important, sensitive matter as drafting security legislation cannot be left to an individual. The government, Home Secretary Douglas Hurd said, must be "in charge." Since the introduction of Shepherd's bill, Hurd has insisted that the government is working on its own draft, to be presented next summer.

In an unprecedented change in parliamentary convention regarding "private" bills introduced by members of the ruling party, the government has ordered Conservatives, "under penalty of death," Shepherd said, to vote against passing his bill into the committee stage.

Among its provisions, Shepherd's bill establishes six categories of national security in which possible violations could occur, and puts the burden on the government to demonstrate that "serious injury" to the state has resulted from unauthorized disclosure of information.

It also establishes for the first time a legitimate public-interest defense for intentionally breaking the secrets law, as well as a media defense for anything that already has been published abroad.