The head of the Jewish Division in the Shin Bet security service, a skullcap wearer who lives in a settlement east of the Green Line, is a big man whose body and face resemble those of Shin Bet chief Yuval Diskin and the MK who represents the settlers, Uri Ariel. This coincidence reflects the mess in which the Shin Bet works in the home arena. If when confronting Palestinians and other Arabs it is swift of foot and agile as a high jumper, when it comes to Jews it has chains on its feet and weights around its neck. The results are commensurate, among them an affair like that of Chaim Pearlman, who is suspected of a double murder; someone who has had contacts of one kind or another with the Shin Bet over the years.

There are Jewish terrorists. They are no different from other terrorists in terms of the danger they present, except in one aspect: They are more dangerous. They are part of the society against which they are plotting, they know how to get close to the centers of power and are familiar with democracy's weak points by dint of their civil rights. They are also up to date with the most modern legal and media-related means of combat. It's easier for them to avoid exposure - if not in terms of intelligence, at least in terms of evidence, without which intelligence is not sufficient. And after their arrest they are skilled at throwing smoke bombs in the fashion of an agent provocateur.

With the caution required on any matter related to systems or people whose basic work is handling agents, fraud and deception, it can be stated that in the Pearlman file the Shin Bet's denials are based on truth. For the past 15 years, since the murder of prime minister Yitzhak Rabin, the Shin Bet has refrained from operating straw organizations designed to attract "isolated terrorists" and get them to carry out terror attacks.

The Shin Bet failed in its short-lived activation of Pearlman a decade ago after the murders for which he is now suspected. Among other things, he did not take a polygraph test, which is supposed to detect lies in his reactions to questions about involvement in terror attacks. But that failure, like the failed attempt to operate him as an agent among his friends, does not put him on the list of famous agents provocateurs in human history, from the days of the czar's secret police up to Avishai Raviv.

Like Yaakov (Jack) Teitel, Chaim Pearlman - if proven guilty (and the Shin Bet was not satisfied with the boasting it recorded and looked for supporting evidence ) - is living proof of an "intelligence failure over the past 10 to 13 years and an intelligence success of the past year," said a top expert on Jewish terror.

The balance really is mixed. It's not exactly the Shin Bet's Pearlman Harbor, but neither is it an achievement to be bragged about. The ongoing failure is more disappointing than surprising. Nationalist murderers, like ideological murderers in general, are usually sophisticated people good at psyching out their opponents - the Shin Bet and the police - no less than the intended victim. If they keep their secret and conduct their lives under the assumption that they are under constant surveillance, they will defeat the system.

Usually terrorists can be defeated only by stratagems: deceiving them, making them believe that a certain activity is being conducted in an innocent context, such as a want ad ostensibly meant for everyone. In this way they don't understand they are acting in a play directed by the Shin Bet. "The Truman Show," but with Pearlman.

The problem is that in the Israeli theater the rules have long been broken and there is no clear division between the director, actors, extras and audience. The Shin Bet does not only attack. It has to invest a great deal of energy in self-defense. In the settlements people harass Shin Bet employees and their families (and sometimes even elderly parents in their hometowns west of the Green Line ). They also harass officials and inspectors, some who break down and leave.

That makes it difficult to carry out the security services' main mission: preventing future terror attacks against VIPs headed by Prime Minister Benjamin Netanyahu and Defense Minister Ehud Barak, and against religious symbols (for example the Temple Mount ) and diplomatic processes. The forecast is gloomy. The Jewish terrorists are liable to imitate their counterparts all over the world with suicide attacks, regardless of the identity and numbers of the dead.

The summer snooze is misleading. In about two months the construction freeze in the settlements will be over. A continuation of the freeze without limiting it to isolated and extremist settlements, a renewal of the diplomatic process toward evacuating settlements, the government's failure in handling the evacuees from Gaza - all this will increase support for the determined hundreds of terrorist extremists who are ready for a violent confrontation.

As a preliminary softening-up exercise, the Shin Bet holds frequent and frank talks with yeshiva heads and other religious leaders. Only at Har Bracha did they encounter total refusal to maintain contact. Compared to the anticipated dangers, the defense establishment will miss the cases that took a long time but were solved in the end, like those of Teitel and Pearlman.