Now that Israel has a broad and secure national unity government, the time is ripe for that government to make a bold peace offer to the Palestinian Authority.
The Palestinian Authority refuses to negotiate unless Israel accepts a "freeze" on settlement building in the West Bank. Israel accepted a 10-month freeze in 2009, but the Palestinian Authority didn't come to the bargaining table until weeks before the freeze expired. Its negotiators demanded that the freeze be extended indefinitely. When Israel refused, they walked away from the table.
There is every reason to believe that they would continue such game-playing if the Israeli government imposed a similar freeze now, especially in light of current efforts by the Palestinian Authority and Hamas to form their own unity government, which would likely include elements opposed to any negotiation with the Jewish state.
That is why Prime Minister Benjamin Netanyahu should now offer a conditional freeze: Israel will stop all settlement building in the West Bank as soon as the Palestinian Authority sits down at the bargaining table, and the freeze will continue as long as the talks continue in good faith.
The first issue on the table should be the rough borders of a Palestinian state. Setting those would require recognizing that the West Bank can be realistically divided into three effective areas:
• Those that are relatively certain to remain part of Israel, such as Ma'ale Adumim, Gilo and other areas close to the center of Jerusalem.
• Those that are relatively certain to become part of a Palestinian state, such as Ramallah, Jericho, Jenin and the vast majority of the heavily populated Arab areas of the West Bank beyond Israel's security barrier.
• Those reasonably in dispute, including some of the large settlement blocs several miles from Jerusalem such as Ariel (which may well remain part of Israel, but subject to negotiated land swaps).
This rough division is based on prior negotiations and on positions already articulated by each side. If there can be agreement concerning this preliminary division -- even tentative or conditional -- then the settlement-building dispute would quickly disappear.
There would be no Israeli building in those areas likely to become part of a Palestinian state. There would be no limit on Israeli building within areas likely to remain part of Israel. And the conditional freeze would continue in disputed areas until it was decided which will remain part of Israel and which will become part of the new Palestinian state. As portions of the disputed areas are allocated to Palestine or Israel, the building rules would reflect that ongoing allocation.
I recently proposed this idea to a high-ranking Israeli official. His initial reaction was mostly positive, but he insisted that it would be difficult to impose an absolute building freeze in any areas in which Israelis currently live. He pointed out that families grow and that new bedrooms and bathrooms are needed in existing structures as a simple matter of humanitarian needs. I reminded him that Mr. Netanyahu has repeatedly stated that Israel is prepared to make "painful compromises" in the interests of peace.
An absolute building freeze would be such a painful but necessary compromise. It might also encourage residents of settlements deep in the West Bank to move to areas that will remain part of Israel, especially if the freeze were accompanied by financial inducements to relocate.
Such a proposal by Israel would be an important first step and a good test of the bona fides of the Palestinian side. Since their precondition to negotiation will have been met by the promise of a freeze (to begin the moment they sit down to negotiate), they would have no further excuse for refusing the Israeli offer to try to resolve the conflict.
The conditional freeze would also test the bona fides of the Israeli government, which would no longer have the excuse that any freeze would risk toppling a fragile coalition that relies on right-wingers who have threatened to withdraw in the event of another freeze. The new national unity government is now sufficiently large and diverse that it could now survive a walk-out by elements opposed to any freeze.
Once the parties reach a preliminary agreement regarding the three areas and what could be built where, they could get down to the nitty-gritty of working on compromises to produce an enduring peace.
These compromises will require the Israelis to give up claims to areas of the West Bank that were part of Biblical Israel but that are heavily populated by Palestinians. It will require the Palestinians to give up any claim to a massive "right of return" for the millions of descendents of those who once lived in what is now Israel. It will require an agreement over Jerusalem, plus assurances about Israel's security in the Jordan Valley and in areas that could pose the threat of rocket attacks like those that have come from the Gaza Strip in recent years.
Both sides say they want peace. In my conversations with both Israeli and Palestinian leaders, I have repeatedly heard the view that "everyone" knows what a pragmatic, compromise resolution will look like. Each side claims that the other side has erected artificial barriers to reaching that resolution.
If the building freeze issue can be taken off the table, one of the most controversial and divisive barriers will have been eliminated. The Israeli government should take the first step, but the Palestinian Authority must take the second step by immediately sitting down to negotiate in good faith.
Mr. Dershowitz is a law professor at Harvard. His latest book is "Trials of Zion" (Grand Central Publishing, 2010).
**A version of this article appeared June 4, 2012, on page A17 in the U.S. edition of The Wall Street Journal, with the headline: A Settlement Freeze Can Advance Israeli-Palestinian Peace.