AS the United Nations General Assembly opens this year, I feel uneasy. An unnecessary diplomatic clash between Israel and the Palestinians is taking shape in New York, and it will be harmful to Israel and to the future of the Middle East.

I know that things could and should have been different.

I truly believe that a two-state solution is the only way to ensure a more stable Middle East and to grant Israel the security and well-being it desires. As tensions grow, I cannot but feel that we in the region are on the verge of missing an opportunity — one that we cannot afford to miss.

The Palestinian president, Mahmoud Abbas, plans to make a unilateral bid for recognition of a Palestinian state at the United Nations on Friday. He has the right to do so, and the vast majority of countries in the General Assembly support his move. But this is not the wisest step Mr. Abbas can take.

The Israeli prime minister, Benjamin Netanyahu, has declared publicly that he believes in the two-state solution, but he is expending all of his political effort to block Mr. Abbas’s bid for statehood by rallying domestic support and appealing to other countries. This is not the wisest step Mr. Netanyahu can take.

In the worst-case scenario, chaos and violence could erupt, making the possibility of an agreement even more distant, if not impossible. If that happens, peace will definitely not be the outcome.

The parameters of a peace deal are well known and they have already been put on the table. I put them there in September 2008 when I presented a far-reaching offer to Mr. Abbas.

According to my offer, the territorial dispute would be solved by establishing a Palestinian state on territory equivalent in size to the pre-1967 West Bank and Gaza Strip with mutually agreed-upon land swaps that take into account the new realities on the ground.

The city of Jerusalem would be shared. Its Jewish areas would be the capital of Israel and its Arab neighborhoods would become the Palestinian capital. Neither side would declare sovereignty over the city’s holy places; they would be administered jointly with the assistance of Jordan, Saudi Arabia and the United States.

The Palestinian refugee problem would be addressed within the framework of the 2002 Arab Peace Initiative. The new Palestinian state would become the home of all the Palestinian refugees just as the state of Israel is the homeland of the Jewish people. Israel would, however, be prepared to absorb a small number of refugees on humanitarian grounds.

Because ensuring Israel’s security is vital to the implementation of any agreement, the Palestinian state would be demilitarized and it would not form military alliances with other nations. Both states would cooperate to fight terrorism and violence.

These parameters were never formally rejected by Mr. Abbas, and they should be put on the table again today. Both Mr. Abbas and Mr. Netanyahu must then make brave and difficult decisions.

We Israelis simply do not have the luxury of spending more time postponing a solution. A further delay will only help extremists on both sides who seek to sabotage any prospect of a peaceful, negotiated two-state solution.

Moreover, the Arab Spring has changed the Middle East, and unpredictable developments in the region, such as the recent attack on Israel’s embassy in Cairo, could easily explode into widespread chaos. It is therefore in Israel’s strategic interest to cement existing peace agreements with its neighbors, Egypt and Jordan.

In addition, Israel must make every effort to defuse tensions with Turkey as soon as possible. Turkey is not an enemy of Israel. I have worked closely with the Turkish prime minister, Recep Tayyip Erdogan. In spite of his recent statements and actions, I believe that he understands the importance of relations with Israel. Mr. Erdogan and Mr. Netanyahu must work to end this crisis immediately for the benefit of both countries and the stability of the region.

In Israel, we are sorry for the loss of life of Turkish citizens in May 2010, when Israel confronted a provocative flotilla of ships bound for Gaza. I am sure that the proper way to express these sentiments to the Turkish government and the Turkish people can be found.

The time for true leadership has come. Leadership is tested not by one’s capacity to survive politically but by the ability to make tough decisions in trying times.

When I addressed international forums as prime minister, the Israeli people expected me to present bold political initiatives that would bring peace — not arguments outlining why achieving peace now is not possible. Today, such an initiative is more necessary than ever to prove to the world that Israel is a peace-seeking country.

The window of opportunity is limited. Israel will not always find itself sitting across the table from Palestinian leaders like Mr. Abbas and the prime minister, Salam Fayyad, who object to terrorism and want peace. Indeed, future Palestinian leaders might abandon the idea of two states and seek a one-state solution, making reconciliation impossible.

Now is the time. There will be no better one. I hope that Mr. Netanyahu and Mr. Abbas will meet the challenge.