JERUSALEM — Under pressure from a key coalition partner, Prime Minister Ehud Olmert has promised to pass legislation for a stronger and more stable government. But Israel will remain a parliamentary democracy and will not adopt the American-style presidential system some reformers have been advocating.

The general consensus in Israel is that the current system of proportional representation and large, unwieldy governing coalitions is not working. The proposed reforms are designed to promote stability, strengthen the executive and legislative branches, and reinforce the separation of powers but without abandoning the European-style parliamentary system.

The inherent instability of the Israeli body politic is underlined by the fact that the country has had no less than 31 governments in 59 years of statehood. The past eight years have seen six defense ministers, seven foreign ministers and eight finance ministers. The new system would make it more difficult to topple a sitting government in mid-term.

Well-intentioned efforts to refine the system in the past have come to naught because political will was lacking. This time, though, the prognosis for change looks good: There is a Knesset majority for many of the proposed reforms and, more importantly, Olmert knows his government will likely fall if he fails to push through the promised package.

The urgency for change gathered steam recently when Strategic Affairs Minister Avigdor Lieberman, leader of the hawkish Yisrael Beiteinu party, gave Olmert an ultimatum: Change the system or Yisrael Beiteinu will bolt the coalition, triggering a process that almost certainly will lead to a government collapse and early elections.

In a meeting at the prime minister’s office last week, Lieberman argued that the Olmert administration had failed to make any lasting imprint on Israeli life, but if it strengthened the ailing system of government that would be an achievement of historic significance.

Lieberman for years has been advocating the introduction of a full-fledged presidential system along American lines. That was one of the main options considered by a special commission of experts established by former President Moshe Katzav in 2005 to analyze the failings of the Israeli system and recommend reforms.

In the end, however, a commission wary of radical change opted for a measured amendment of the current system rather than the adoption of something different and untried in Israel.The Knesset’s Law, Constitution and Justice Committee, which has also been debating reform for years, concurred.

Both committees were influenced by the resounding failure of Israel’s last electoral experiment: the direct election of the prime minister, which contrary to expectations led to a strengthening of the smaller parties.

The new reform package contains the following elements:

* After an election, the leader of the largest party automatically becomes prime minister. This will encourage voting for larger parties with realistic candidates for prime minister such as Benjamin Netanyahu’s Likud, Ehud Barak’s Labor or Olmert’s Kadima. Secondly, since the prime minister would have been elected, wheeler-dealer smaller parties could not play one candidate against another in coalition negotiations.

* Introduction of the so-called “Norwegian Law” in which legislators appointed to the government automatically resign from the Knesset, making way for the next in line. This would promote stricter separation of powers and enable all 120 members of the Knesset to devote themselves full-time to the business of the legislature.

* “Constructive no confidence.” To unseat an incumbent prime minister, at least 66 Knesset members would have to vote against him or her and agree on a successor. This would make it much harder to topple a government in mid-term, since the chances of opposition members from left and right coalescing around the same alternative candidate are not high. It also would make it more difficult for coalition partners to hold a prime minister to ransom by threatening to bring him down.

As things stand, 61 Knesset members can unseat a prime minister without having to unite around a successor.

* Raising the threshold for election to the Knesset from 2 percent to 3 percent. This would eliminate very small parties or force them to merge with like-minded larger groupings.

* Passing the budget for the coming year by Dec. 31 or face new elections. The thinking is that this would ensure that the budget is passed on time and eliminate the current three-month extension period.

The president’s commission made another major recommendation: That the country be divided into 17 constituencies and that 60 of the Knesset members be elected in regional elections and 60 according to party slates. Now all 120 Knesset members are elected on party slates in a system of pure proportional representation.

This amendment also would have tended to strengthen the larger parties, as well as make the constituency-elected Knesset members directly accountable to their constituents.

The problem is that the proposal, which has been around since the mid-1950s, still does not have a Knesset majority. The smaller parties, fearing they stand to lose the most, are adamantly against any such change.

According to Knesset member Menachem Ben Sasson of Kadima, the chairman of the Law Committee, he will not be able to muster a majority for any form of constituency elections and therefore it will not be part of the legislative package he is preparing.

Ironically, the change in the system is being spurred by the very coalition pressures it seeks to eliminate. Olmert’s coalition has 77 supporters in the Knesset, but if Lieberman pulls out his 11 Yisrael Beiteinu legislators, the right-tending, fervently Orthodox Shas is likely to withdraw its 11 as well — a move that almost certainly would spark new elections.

As for the hawkish Lieberman, he needs to show his voters why he has remained in a coalition that is talking peace with the Palestinians on the basis of the 1967 borders.

High-profile amendments of the system making for stronger government would provide a convincing answer.

Ever since Lieberman joined the relatively dovish coalition, he has been losing support in a big way. The question he and Olmert will have to ask themselves, though, is whether the changes they are advocating will actually strengthen them in an election or play into the hands of key rivals such as Netanyahu, who might sweep to power on the coattails of a system favoring larger parties like the Likud and provide the new incumbent with a stronger power base from which to govern as he sees fit.