The Islamic Resistance Movement, Hamas, has expanded beyond the Gaza Strip and West Bank to enlist a network of Israeli Arabs willing to carry out attacks against Israel, according to Palestinian officials and senior Israeli intelligence officers.

The enrollment of Israeli Arabs in anti-Israel operations, the sources said, has come in response to increasingly successful moves by Israeli, U.S. and Palestinian intelligence services to repress the Hamas military wing in both Palestinian- and Israeli-controlled portions of the Gaza Strip and the West Bank. Underground Hamas militants from those areas have been responsible for most recent terrorist attacks against Israeli targets.

Senior Israeli intelligence officials analyzing the Hamas move into Israel said they are still working to gauge the size of what one described as a "new battle front with soldiers we did not know about." However, he said, the network among Israeli Arabs is already believed to be "large enough to be very dangerous" and would be able to operate much more easily than previous Hamas cells.

Israeli officials said they had not seriously considered Israeli Arabs to be a threat until two car bombs exploded in northern Israel on Sept. 5, hours after the conclusion of the most recent stage in Israeli-Palestinian peace talks. Three men in the cars--which exploded prematurely and killed their occupants--were Arabs from Israel. By Saturday, nine Israeli Arabs were being held in the investigation; today, the government announced the arrest of another Israeli Arab, who it said confessed to helping set up the explosives with the aim of placing them on buses traveling to Jerusalem.

"Maybe they made mistakes this time, but it is a beginning," an Israeli intelligence officer said. "They will learn quickly, especially with outside help."

Four days before the car bomb blasts, Hamas claimed responsibility for the fatal stabbing of a Jewish couple while they were hiking in northern Israel. Initially, Israeli intelligence officers dismissed that claim; now they say it may be genuine.

There have been occasional attacks against Jews by Israeli Arabs for political reasons, but, as far as is known, there had been no militant Islamic network in Israel using terrorism as a tactic.

"This is our responsibility to stop, but we are not able to do it yet, because we don't have people in the field in the right places or with the right information," said a senior Israeli intelligence officer.

Israeli Arabs--Palestinians who remained in Israel when the Jewish state was formed in 1948 and who have Israeli citizenship--are far less restricted in their movements inside Israel than are Palestinians from Gaza and the West Bank, who cannot enter Israel without permission. In addition, the officials said that while Palestinian authorities have been combating terrorist groups based in the areas under Palestinian control, Palestinian police will not be of great help in stopping attacks carried out by Israeli Arabs.

About 1 million Israelis are Arabs, close to 20 percent of the population. Most are considered unthreatening to Israel, although they do not serve in the armed forces and often suffer discrimination in health care, housing, education and employment.

The three men who died in the car bomb blasts had ties to the radical wing of the Islamic Movement of Israel, which its leaders describe as an organization dedicated to promoting Muslim values. The moderate wing of the group quickly condemned the attacks, and its leaders accused Israeli politicians of searching for pretexts to move against Israeli Arabs.

On Sunday, Israel's Internal Security Minister, Shlomo Ben Ami, heard recommendations from his top aides on steps to be taken against Israeli Arab organizations in light of the new Hamas efforts. No details of the meeting or its conclusions were made public.