THE CLEAR MESSAGE sent to Israeli Prime Minister Ehud Barak from an ultra-Orthodox coalition partner called Shas is that the broad domestic support Mr. Barak seeks for the peace process has a price--and it isn't cheap. With only a week before the Syrian-Israeli negotiations are to resume, Shas--which represents Israeli Jews of Middle Eastern origin--threatened to walk out of Mr. Barak's government unless he coughed up millions of dollars to help bail out the party's ailing private school system. To avert a crisis, Mr. Barak essentially paid up.

This sort of all-but-open extortion is far from new in Israel. At the same time, Shas's ability--and its willingness--to provoke a coalition crisis so soon before negotiations are to resume emphasizes the extent to which Mr. Barak's foreign policy maneuverability is tied to his ability to satisfy domestic constituencies on unrelated matters.

Israel's electoral system has long ensured the ability of swing parties--generally religious parties--to support governments on a kind of fee-for-service basis. Mr. Barak may have been elected with a mandate that, in the context of Israel's sharply divided electorate, was quite sweeping. But even as he personally received 57 percent of the vote for prime minister, his party actually lost ground in the Knesset and by itself now controls fewer than half of the seats required to form a government. This makes Mr. Barak, despite his enormous personal victory, heavily dependent on the support of parties with agendas different from his own and radically different from one another's.

Shas, which controls 17 seats, is important to Mr. Barak--for its size, for its dovish peace posture and for representing a constituency that tends to be hostile to Mr. Barak's own center-left movement. With one foot in the government and one in the opposition, Shas can keep Mr. Barak from taking its support for granted. This stance threatens mischief in the peace process, particularly on the Syrian track. Apparent instability in the Israeli government could induce caution in the Syrians. And Shas's cooperation may well prove necessary to ensure that any peace agreement with Syria passes the national referendum Mr. Barak has promised.

Still, the government is stabler than it looks. Shas, by itself, cannot bring down Mr. Barak's government, as there are other parties--nominally in the opposition--that could be brought in to maintain a majority. This means that Shas has a powerful incentive to remain part of the government, the spigot on which the party's patronage politics depends. Crises may erupt, but--as with this one--all sides have real interests in making sure they get resolved.