An energetic and ambitious former spy who says that "guy issues" have clouded crucial Israeli government decisions is being urged to assume the country's prime ministership as Ehud Olmert's rule appears to be on the brink of collapse.

For Tzipi Livni, her role as vice-prime minister means that in an emergency - such as the sudden illness that snatched the former prime minister, Ariel Sharon, from office last year - the position would automatically be hers.

More likely is that Olmert, Israel's 61-year-old prime minister, who is known for his dedication to jogging, will be forced out by criticism - surrounding his handling of last year's war in Lebanon and a separate corruption scandal.

Pressure on him reached a new intensity last week with the resignation of the chief of the general staff, Lt-Gen Dan Halutz, for the Israeli army's failures against Hezbollah in Lebanon. Since then, Olmert has faced a barrage of calls from politicians on the Left and Right to follow suit. One veteran left-wing MP, Yossi Beilin, demanded that the prime minister step aside specifically to make way for Livni.

Livni is a deeply private 48-year-old mother of two. One of her children is in compulsory military service, while the other is still at school. On the political stage, however, she cuts a composed and stylish figure, without resorting to power dressing. "She is not as aggressive as most of the women politicians I've met,"said Colette Avital, a fellow MP and former diplomat.

Nonetheless, she is not shy of declaring her ambitions to become the country's first female leader since Golda Meir and appears determined not to take over by default. Refusing to rule out a challenge to Olmert, she has been relentlessly burnishing her credentials and insisted recently that she was "qualified to be prime minister''.

A Livni challenge would be enormously popular with supporters of the centrist Kadima party that Olmert still nominally leads. In a recent poll, only eight per cent of Kadima voters wanted him as leader - putting him in humiliating fifth place behind "none of the above'', which scored 12 per cent. Livni topped the poll with 50 per cent.

She is already looking and acting like a leader. While Olmert noted after the summer war in Lebanon that "a prime minister doesn't have to have an agenda, he just has to run a country'', Livni has been actively drawing up plans for the future of Israel's most crucial policies.

She has come up with her own ideas for establishing peace with the Palestinians, adapting the US-backed "road map for peace"to try to free it from stagnation.

Her frequent trips to America have helped raise her profile. As foreign minister leading Israel's rallying cry against the nuclear ambitions of Iran, she has effectively become her country's most prominent figure on the international stage. When the Israeli newspaper Haaretz reported last week that secret peace talks had been under way for two years between Israel and Syria, she was named as an instigator.

Covert diplomacy

Such covert diplomacy would come naturally to Livni, who worked for Mossad, Israel's foreign intelligence service, for four years in the 1980s, before becoming a lawyer.

She was first elected to the Knesset as a member for the right-wing Likud party only eight years ago, but since then, with astute politicking, her rise has been assured.

Her most powerful ally was Ariel Sharon, for whom she helped broker the controversial Jewish pullout of the Palestinian Gaza Strip with his internal Likud party critics.

When Sharon left Likud to form Kadima, Livni went with him, becoming the party's number three. When Sharon was plunged into a coma by a stroke in January last year, she rallied behind Ehud Olmert and became number two. Now she appears to be aiming higher still.

"There is no question that she's ambitious for the top job," said Yael Yishai, a professor of political science who specialises in the role of women in Israeli politics. "She's very capable, very talented, very shrewd and knows what she wants.''

But Prof Yishai predicted that Livni would face serious obstacles. "Israeli politics is very tribal and you need military and social connections, which she doesn't have and can't make at her age. She's a bit of a loner,"she said.

Livni has revealed that she has had to struggle against the boys' club atmosphere at the top levels of Israeli decision-making.

"Sometimes there are guy issues," she said in a recent interview. Asked if there had been a "guy problem" in the conduct of the Lebanon war, she replied: "Not only in the war. In all kinds of discussions, I hear arguments between generals and admirals and such and I say, 'Guys, stop it'.''