Israel's heart-wrenching bombing of a Lebanese village on Sunday marred Secretary of State Condoleezza Rice's weeklong mission to halt the fighting between Israel and Hezbollah. President Bush stressed the need for a "sustainable peace" in the volatile region.

Rice's meeting with Lebanon's prime minister was scrapped at the last minute, and the airstrike led her to plan a Monday return to Washington to work on a political solution.

In one of her strongest statements on the need to end the conflict, Rice said, "I think it's time to get a cease-fire."

CountryWatch: Israel

Rice hoped to engage in a weekend "give-and-take" with Israeli and Lebanese officials and acknowledged such a dialogue would prove difficult. Then Israel's airstrike on Qana, Lebanon, derailed her work. The attack early Sunday that killed more than 50 civilians was the deadliest in the 19 days of fighting. Most victims were children.

Rice expressed sympathy for the "terrible loss of innocent life," but did not call for an immediate cease-fire. She maintained the U.S. position that Lebanon and Israel first must settle border disputes, prisoner exchanges and other tough questions.

Bush, at a White House sporting event for youngsters, said, "Today's actions in the Middle East remind us that friends and allies must work together for a sustainable peace particularly for the sake of children."

Rice acknowledged the "pretty political and dicey circumstances" in which she found herself.

"Too many innocent people — Lebanese and Israeli — have suffered," Rice said. "Too many people have lost their lives. Too many families are homeless. And too many children have been killed, injured or are living in fear for their lives."

The attack came at an especially inopportune time for Rice. Arriving Saturday for a second visit in a week to the Middle East, she hoped to broker an agreement that could serve as a foundation for a U.N. Security Council resolution.

International pressure is growing for the United States to call for a quick truce, even as Israeli officials say its military may need 10 days to 14 more days to accomplish its objectives against Hezbollah, a Lebanese Shiite political party with its own militia.

A French-sponsored draft resolution, circulating this weekend among council members, calls for an immediate halt to fighting and seek a wide new buffer zone in south Lebanon monitored by international forces and the Lebanese army.

A U.S. official, who spoke on condition of anonymity about the diplomatic situation, said Rice would work from Washington on the U.N. resolution.

In Beirut, Prime Minister Fuad Saniora said the attack on Lebanese civilians showed that a cease-fire is the only option. "There is no place at this sad moment for any discussions other than an immediate and unconditional cease-fire as well as international investigation of the Israeli massacres in Lebanon now," he told reporters.

Israeli Prime Minister Ehud Olmert expressed "great sorrow" for the deaths, but blamed Hezbollah guerrillas for using the area to launch rockets at Israel.

Fighting that began after Hezbollah captured two Israeli soldiers has left more than 750 people dead; the vast majority are Lebanese civilians.

The Bush administration has stood by Israel's efforts to go after Hezbollah. But administration officials also have tried to find ways to support the fragile Lebanese democracy, which the U.S. sees as part of its vision for "the new Middle East" of healthy, elected governments.

White House spokesman Tony Snow said the Qana attack did not change U.S. policy, but will hasten efforts to end the violence in a sustainable way. "It clearly does have impact," Snow said.

James Dobbins, a former Bush administration envoy to Afghanistan, said the attack will intensify pressure on the U.S. to join other nations in rallying behind a cease-fire.

"It does underscore the degree to which the war is escalating, passions are increasing and American and Israeli isolation is deepening," said Dobbins, who now heads military analysis for the Rand Corp., a research institution.

The State Department's third-ranking official reaffirmed the White House's position that Israel has the right to defend itself.

"Israel was attacked two weeks ago. It was Hezbollah who started this and crossed the blue-line," Undersecretary of State Nicholas Burns said in Washington.

In a diplomatic push from Jerusalem, Rice had an evening meeting with Israeli Prime Minister Ehud Olmert and dinner with Foreign Minister Tzipi Livni. She planned to see Defense Minister Amir Peretz on Monday.

She also called Bush, U.N. Secretary-General Kofi Annan and the European Union's foreign policy chief, Javier Solana.

A senior administration official, also speaking on condition of anonymity, said U.S. officials also were talking to Lebanese leaders.

Indicating frays in the U.S.-Lebanese relationship, officials from both countries publicly disputed which side canceled Rice's trip to Beirut to talk to Saniora.

Angry Lebanese officials say they told Rice not to come. Said Snow: "Rice called him and said that she would cancel the meeting."

Rice's aides sought to put a distinctly U.S. mark on her diplomatic efforts after a surprise visit last Monday to Lebanon's capital, her first stop on the weeklong trip.

"With this stop now, we — the United States — are firmly in the picture in leading the diplomacy, with the secretary of state doing that job," Assistant Undersecretary David Welch said at the time.

But Rice and her entourage struck a more somber tone Sunday.

Rice said she is working with all parties to try to stop the violence. "Emotions are understandably running high on all sides," she said.

She also tried to stress the progress made during last Wednesday's conference in Rome, where representatives of 18 countries gathered to discuss Lebanon. In broad terms, they agreed on the urgent need to work for a cease-fire, provide humanitarian aid, establish a peacekeeping force and disarm Lebanese militias such as Hezbollah.

"We are making real progress on the political framework and believe the parties are coming together," Rice said on Sunday.

Yet Trita Parsi, a Middle East specialist at Johns Hopkins University, said the Middle East crisis is sending a terrible signal to the Arab world: "It doesn't matter how much you come to the United States aid, the U.S. will always side with Israel," he said.