The Bush administration welcomed, with reservations, cease-fires declared Sunday by Palestinian militant groups in their long fight against Israel.

"Anything that reduces violence is a step in the right direction," said White House spokeswoman Ashley Snee, who spoke by telephone from Washington to reporters with President Bush at his Texas ranch.

Still, she said, "parties have an obligation to dismantle terrorist infrastructure" under a U.S.-brokered "road map" that calls for establishing a Palestinian state by 2005. "There is still more work to be done."

Snee said national security adviser Condoleezza Rice, in the Middle East for the cease-fire announcements, again extended an invitation to Palestinian Prime Minister Mahmoud Abbas to visit Bush in Washington soon. The president invited Abbas previously. A Palestinian official in the region said Abbas accepted, but Snee said no date has been set.

Abbas would be the first Palestinian leader in three years at the White House. Bush has worked to sideline longtime Palestinian leader Yasser Arafat, who visited several times during President Clinton's tenure. Arafat is tainted by terror, Bush says, but he has had Israeli Prime Minister Ariel Sharon to the White House several times.

On June 4, both Sharon and Abbas, standing beside with Bush, committed to moves outlined in the formula toward peaceful coexistence between independent states, Israel and Palestine.

Since then, Bush has dispatched Secretary of State Colin Powell and now Rice to the region to push the plan forward. Rice met with Abbas on Saturday and on Sunday with Israeli Prime Minister Ariel Sharon.

The cease-fire announcements by the three major groups that have claimed months of bombing of Israeli targets came as Israelis and Palestinians worked out details of an Israeli troop pullback in the Gaza Strip. Peace has been fragile in the Middle East for years, however, and new attacks on Israel by renegades, or Israeli military strikes on suspected militants could quickly rekindle violence.

Sen. Joseph Biden, senior Democrat on the Senate Foreign Relations Committee, said on Fox News Sunday that he was not optimistic about the cease-fire agreement. He added: "I think the Israelis are prepared to take a chance on it."

The Bush administration's tepid reaction to the agreement by the militant groups Hamas, Islamic Jihad and Fatah to end nearly three years of Israeli-Palestinian fighting tracked closely with the cool reception the cease-fire announcement received from Sharon. Israel wants the militants disarmed and arrested to avoid further attack. That's a demand the Palestinian Authority hasn't accepted, and the militants bitterly reject.

Biden said part of his skepticism about the cease-fire comes from his distrust of Hamas, "a flat-out terrorist organization."

He said the United States and other nations should help the Palestinian Authority financially so that Abbas' administration could pay for social services for the Palestinian people that Hamas underwrites. That would allow Abbas to demonstrate to the people that they are no longer dependent on Hamas and can count on him to provide water, sewer service, hospitals and other services.