JERUSALEM - Israel's soft-spoken foreign minister learned politics early as the daughter of a prominent hard-line activist. After a meteoric rise in recent years, Tzipi Livni emerged yesterday as the biggest threat to force out Prime Minister Ehud Olmert.

A close ally of former Prime Minister Ariel Sharon, Livni followed a similar political metamorphosis. She started as a hawk, rejecting compromise with the Palestinians, but evolved into a centrist, advocating creation of a Palestinian state while safeguarding Israel's security.

Livni, 48, is a stark contrast to Olmert. Perhaps reflecting her time as a Mossad agent from 1980 to 1984, she measures her words and maintains a calm exterior, while the cigar-chomping Olmert enthusiastically pumps hands, claps backs, and lets fly with sometimes costly inexact phrases.

An example of Livni's low-key style was the careful phrasing of her demand to Olmert yesterday.

"I told him that resignation would be the right thing for him to do," she said, setting herself up to step in and become Israel's second female prime minister, after Golda Meir.

Born in Tel Aviv, Livni is much more comfortable speaking in Hebrew than in English, but during her year as foreign minister, she has received high marks from diplomats for her ability to communicate Israel's policies. Her official resume says she also speaks French.

Livni earned a law degree at Bar Ilan University near Tel Aviv and served as a lieutenant in the Israeli army before joining the Mossad. She is married and has two children.

Livni has quietly worked her way up through the ranks of Israeli politics, making few enemies and winning many admirers. She started out as a member of the hard-line Likud Party, following the lead of her father, Eitan Livni, a pre-state underground fighter turned hawkish politician. She was elected to parliament as a Likud member in 1999.

She bolted Likud along with Sharon to form the Kadima Party, serving in his cabinet overseeing the absorption of immigrants. She catapulted to foreign minister when Sharon was felled by a stroke in January 2006 and Olmert took over as prime minister.

While she lacks an electric presence, Livni consistently scores well in popularity polls, projecting a calm competence that resonates with an Israeli public worn down by years of conflict.

And bubbling under her sober demeanor is a droll sense of humor.

During an official trip Livni made to Moscow with Sharon, Russian President Vladimir V. Putin remarked that the prime minister had brought along a beautiful cabinet minister to seduce Russian Jews into moving to Israel.

Later, when a reporter asked how she intended to "seduce" a million Russian immigrants, Livni deadpanned: "One at a time."