Saudi Arabia today called on Islamic militants to surrender to authorities within a month under a new amnesty program or face the government's "unmitigated power and unhesitating will."

The amnesty was announced in a rare televised statement by Crown Prince Abdullah, the kingdom's de facto ruler, who said he was speaking on behalf of King Fahd.

The offer was directed to adherents of the al Qaeda terrorist network, which has been waging an escalating campaign of suicide bombings, kidnappings and assassinations directed against Westerners, the oil industry and the royal government.

Last week, militants of a group calling itself the Fallujah Squadron of al Qaeda in the Arabian Peninsula beheaded an American hostage, Paul M. Johnson Jr., a 49-year-old employee of Lockheed Martin Corp., and sent photographs of his body to an Islamist Web site.

Hours later, Saudi security forces killed the suspected leader of al Qaeda in the kingdom, Abdulaziz Muqrin, and three of his comrades in a raid in the Saudi capital, Riyadh. At the same time, the government announced the arrest of 12 persons suspected of having links to recent terrorist attacks.

According to a translation by the official Saudi Press Agency, Abdullah said, "In deference to instructions from God Almighty, we announce, once and for all, that the door of pardon is open, and return to the right is possible, and resort to the rules of the Islamic Sharia for whoever deviated from the road of right is the wise way."

He said the government was offering "a chance for whoever belongs to the misguided group and is still at large following involvement in terrorism operations to repent, plead guilty and voluntarily surrender within one month from the date of this address."

Wearing a white keffiyeh headdress and sitting in a leather chair as he solemnly read his four-minute speech, Abdullah said that those who accept the amnesty "will be immune from prosecution and will be treated according to the Sharia law in relation to violated rights of third parties." He did not elaborate on this point, but added:

"All of you know that we are not speaking from a position of weakness, but we offer an alternative to those who might make use of it. We, government and people, want to open the door of penance and security for whoever is wise enough to take it; and whoever takes the chance will be safe. But should he be obstinate, he will face a resolute force; for in retaliation our tolerance will not prevent us from exercising unmitigated power and unhesitating will."

In addition to being heir to the throne of Fahd, his ailing half-brother, the crown prince also holds the titles of deputy prime minister and commander of the National Guard.

A spokesman for the Saudi Embassy in Washington said that Abdullah's offer was not a blanket amnesty. In Riyadh, the Reuters news agency quoted a security source as saying that the message was aimed at lower-level al Qaeda sympathizers who had not yet committed violent acts and that those who had participated in killings would not escape justice.

Earlier, the Saudi foreign minister, Prince Saud Faisal, said the death of Muqrin represented a major blow for al Qaeda in the kingdom, but he cautioned that the group remains dangerous.

"Getting rid of one cell doesn't mean this issue is over," he told a news conference in Jeddah. "It is a strong blow, but when the danger is over, we will announce it."

Al Qaeda supporters, who have killed at least 85 civilians and police in Saudi Arabia, have aimed their attacks lately at disrupting the wealthy kingdom's oil industry and driving out the foreign workers on which it depends. The United States and Britain alone have more than 60,000 citizens in Saudi Arabia.

One of the bloodiest recent attacks, a hostage-taking and shooting spree in May by militants posing as security men in the oil center of Khobar, left 22 civilians dead.

In an annual address to Saudi Arabia's Consultative Council on Sunday, Fahd vowed, "We will not allow a wicked group driven by a deviant ideology to destabilize the kingdom's security."