Foreign Minister Tzipi Livni, in a seeming about-face, indicated she might be willing to come on board a Netanyahu government.

But Livni, a centrist, would certainly exact a high price: sharing the prime minister's job she so fervently sought with a reluctant Netanyahu. Should he balk, his alternative would be an unstable coalition of right-wingers sure to collide with the Obama administration and its ambitious plans for ending 60 years of conflict between Israel and the Palestinians.

Netanyahu urged Livni of the governing Kadima Party and Defense Minister Ehud Barak of the Labor Party to join his government.

"I call on the members of all the factions ... to set politics aside and put the good of the nation at the center," Netanyahu said during a low-key ceremony at the president's residence in Jerusalem.

Friday's decision by Israel's ceremonial president, Shimon Peres, to tap Netanyahu ended days of speculation and gave Netanyahu six weeks to put together a ruling coalition.

Peres had been meeting with political leaders as he decided which candidate would be given the task of cobbling together a new coalition in the aftermath of Israel's national election last week.

The choice of Netanyahu was cemented on Thursday when Avigdor Lieberman, who heads the hawkish Yisrael Beiteinu (Israel Our Home) party, endorsed him.

Lieberman's party, which based its campaign on requiring Israel's Arab citizens to swear loyalty to the Jewish state or lose their citizenship, came in third place in the Feb. 10 election, after Kadima and Netanyahu's Likud. That essentially allowed him to determine whether Netanyahu or Livni would be able to muster the backing of a majority in parliament.

Kadima edged out Likud in the election, capturing 28 seats to Likud's 27. But Likud is in a better position to put together a coalition because of gains by Lieberman and other hard-line parties.

Emerging from her meeting with Peres, Livni said she would not join a hard-line government and was prepared to sit in the opposition "if necessary."

"I will not be able to serve as a cover for a lack of direction. I want to lead Israel in a way I believe in, to advance a peace process based on two states for two peoples," Livni said.

With Livni out, Netanyahu might have little choice but to forge a coalition with nationalist and religious parties opposed to peacemaking with the Palestinians and Israel's other Arab neighbors.

This could set Israel on a collision course with the U.S., the Jewish state's top international patron, and its new president, who has vowed to make Mideast peace a top priority. Netanyahu's hold on power would be more tenuous in a narrow coalition of rightists, where his allies could bring down the government in the face of any concession for peace.

Putting together a broad, centrist government would be a tall order for Netanyahu, however.

Livni has said she will not join Netanyahu in a government unless she can be an equal partner, presumably through the sort of "rotation" agreement Israel has tried in the past in which an election's top two winners each get to be prime minister for half of the government's four-year term.

Netanyahu, however, has ruled out any such arrangement.

As the political wrangling in Israel gained momentum, sporadic violence continued in Gaza in the absence of a long-term cease-fire between Israel and Hamas. Militants fired mortar shells at an Israeli patrol along the Gaza-Israel border Friday, Israeli defense officials said, and the troops returned fire. There were no injuries reported.

Egypt has been trying to mediate a truce since Israel ended its Gaza offensive Jan. 18. Hamas wants Israel to open Gaza's blockaded border crossings, while Israel wants a halt to arms smuggling and the return of a soldier captured in 2006.

Netanyahu has said Israel must topple the Hamas government in Gaza and says Israel halted the Gaza offensive too soon.