Prince Turki al-Faisal, brother of Foreign Minister Saud al-Faisal, said Secretary of State John Kerry's diplomacy was praiseworthy, but a lasting two-state solution, with an independent Palestine alongside Israel, would be forged only if Obama was willing to be the heavy and pressure both sides to make needed concessions.
"Mr. Kerry is devoting a lot of time and energy," Turki told the World Policy Conference in Monaco on the French Riviera.
"But we'll see how far he gets if the president doesn't put his full support behind it," Turki said.
Turki, a former Saudi intelligence chief and ambassador to Washington, told the gathering of mostly European, Middle Eastern and North African officials Sunday the United States was like a big bear and needed to threaten Israeli and Palestinian Authority leaders into an agreement.
He said this fear approach would give both sides an excuse to blame Washington for making difficult but needed compromises on key issues. Those issues include Jerusalem, security arrangements, the right of Palestinian refugees to return to the new Palestinian state and land swaps, he said.
"Unfortunately, the big bear has not proven to be very bearish-like recently," Turki said in remarks quoted by the New York Times.
The Washington bear "has to not only bare his teeth, but also extend his claws" to get an agreement, said Turki, who no longer has a government position but is often an unofficial spokesman of the Saudi royal family and King Abdullah.
Turki also said Saudi Arabia has seen several "red lines" put forward by Obama turn "pinkish as time grew, and eventually ended up completely white."
And "if the president retreats from his position on compromise along the 1967 borders, as he did on his red line on use of chemical weapons by [Syrian President Bashar] Assad, then the whole enterprise of peace between the Arabs and Israel will evaporate," Turki said.
Obama has said for 2 1/2 years the prevailing borders before the 1967 Arab-Israeli war -- adjusted with "mutually agreed land swaps" to account for postwar Israeli settlements in the West Bank -- should be the basis of an Israeli-Palestinian deal.
During the war, Israel took effective control of the Gaza Strip and the Sinai Peninsula from Egypt -- known then as the United Arab Republic -- the West Bank and East Jerusalem from Jordan and the Golan Heights from Syria.
The White House had no immediate comment on Turki's remarks.
In the past administration officials have said Obama was "closely engaged" in the Kerry-led Middle East peace process.
Turki also said a failure by Washington and the United Nations to take decisive steps to end the Syrian civil war bordered on "criminal negligence."