PARIS — Leaders of 43 nations with nearly 800 million inhabitants inaugurated a new “Union for the Mediterranean” on Sunday, meant to bring the northern and southern countries that ring the sea closer together through practical projects dealing with the environment, climate, transport, immigration and policing.

But the meeting was also an opportunity for President Nicolas Sarkozy, of France, to exercise some highly public Middle East diplomacy by bringing President Bashar al-Assad, of Syria, out of isolation for an Elysee Palace meeting and by playing host to a session between Prime Minister Ehud Olmert, of Israel, and the Palestinian president, Mahmoud Abbas.

While initial accomplishments are likely to be vague, the meeting represented an end to the diplomatic isolation of Assad, who has been ostracized for his alliance with Iran, for his support for Palestinian groups classified by the United States and the European Union as terrorist.