Jerusalem ? Israel’s surprising strike at an alleged Islamic Jihad base in Syria — in response to a suicide bombing by the group — threatens to widen the conflict with the Palestinians and draw in an old enemy, whose frontier with Israel has been quiet for 30 years.

The strike early Sunday underscores Israel’s frustration with its inability to end three years of unrelenting Palestinian militant attacks despite a massive and continuing military effort in the West Bank and the Gaza Strip.

If Syria does not respond militarily to the strike — as it appears it won’t — Israel will have succeeded in serving notice that it is prepared to strike at nations supporting militant groups as part of its campaign to halt violence against the Jewish state.

“The attack today is to show the Islamic Jihad they will receive no sanctuary, regardless of where they are,” said Raanan Gissin, an adviser to Israeli Prime Minister Ariel Sharon. “This is also a very clear message to Syria. Despite U.S. demands to close all the (militant) bases, nothing has been done. They have to comply with what they promised.”

Syria has been accused by the United States of harboring terror groups and allowing militants to cross its border into Iraq to kill U.S. soldiers.

After Saturday’s suicide bombing by Islamic Jihad, in which 19 bystanders including several children were killed in a crowded beachfront restaurant in Haifa, the Israeli government was under strong pressure at home to deliver a dramatic response.

Israel apparently calculated that Syria would not retaliate and that the United States, upset with Syria for a failure to confront militants, would not be overly angry at the bombing. The Bush administration called for restraint by both sides.

But the move was not without risk and could destabilize what has been a relatively peaceful frontier. There has been relatively little fighting since the 1973 Yom Kippur War — which broke out 30 years ago today — when Syria tried to reclaim the Golan Heights that it lost in the 1967 Mideast War.

Syrian President Bashar Assad, who took office in July 2000 after the death of his father, Hafez, has not been tested in battle against Israel and is widely seen as unlikely to risk a major confrontation now.

“Syria is not in a military position to do serious damage to Israel without massive Israeli response,” said Gerald Steinberg, a political science professor at Bar Ilan University.

Other than the Palestinians, Syria remains almost the last of Israel’s traditional enemies. Israel has signed peace treaties with Egypt and Jordan, and the Saddam Hussein regime in Iraq was eliminated by U.S. forces this year.