Extreme right-wing Jewish activists in the West Bank have moved from spontaneous acts against Arabs - following the demolition of Jewish homes by Israeli authorities, or terror attacks against Jews - to organized planning that includes use of a database of potential targets, according to new analysis by the Shin Bet security service.

The small groups of Jewish extremists are difficult to infiltrate and carry out surveillance on Arab villages and collect information about access points and escape routes in the villages. They are also collecting information about left-wing Israeli activists.

A left-wing activist was apparently the latest "price tag" victim on Monday, when threatening graffiti against a Peace Now leader was discovered on the front of her Jerusalem apartment and in a nearby stairwell. The incident follows last week's vandalism attack on an Israel Defense Forces base in the West Bank, in apparent revenge for the demolition of unauthorized Jewish construction in settlement outposts there.

Sources in the Shin Bet noted that the planned attacks against Arabs and left-wing Israelis constitute terrorist activity, for all intents and purposes.

The Peace Now activist, who asked not to be identified, said her neighbors woke her Monday morning to inform her of the graffiti. "Peace Now, the end is near," read one slogan. "Migron forever," read another, in reference to the unauthorized West Bank outpost where the demolition of houses was carried out last week. The most threatening content, however, made a specific call for the Peace Now activist's murder.

"We know there is someone trying to scare us," the activist said yesterday, adding that senior IDF officers have experienced similar incidents. The police are dealing with the matter, she said, expressing confidence that those responsible will be found. The Jerusalem police have not yet made any arrests in the case.

In response to the graffiti attack, the Peace Now organization said: "The incidents make it necessary to take strong steps against what appears to be a new Jewish underground."

The Peace Now activist whose apartment building was vandalized is a well-known left-wing personality who is closely identified with her organization and is involved in the group's monitoring of Jewish settlement activity in the West Bank. She asked that her name not be publicized in connection with the incident out of concern that she could be threatened directly. Nonetheless, she went to work as usual yesterday visting Palestinian villages in the Ramallah area to take pictures of so-called "price tag" activity.

On Sunday evening, a demonstration was held in front of the Prime Minister's Residence by settlers from Migron whose homes had been demolished the week before by the IDF and the police. Others who joined the protest brought pieces of the demolished homes with them.

"A despicable act was carried out in Israel last week," said Itai Harel, one of the founders of Migron. "A large force came in the dead of night and left 12 children without a roof over their heads. The games are over at Migron," he added. Several hours after the demonstration, the graffiti incident occurred at the apartment, which is near the Prime Minister's Residence.

Since the demolition of three homes at Migron on September 5, there has also been a marked rise in acts of violence against mosques and Palestinian property. On the night on which the three houses were razed, an arson attempt was carried out at a mosque in the West Bank village of Kusra, near Nablus.

Last Wednesday, IDF jeeps and other army equipment were vandalized. On Thursday, cars were set on fire in the West Bank village of Qabalan and graffiti was spray painted on the facade of a mosque in the village of Yatma. The following day, the facade of a mosque was vandalized with graffiti in the Palestinian town of Bir Zeit, and yesterday grapevines belonging to Palestinians from Halhul were damaged not far from the settlement of Karmei Tsur. Cars were also torched in Arab villages near Migron.