By Patrick Worsnip

UNITED NATIONS, April 27 (Reuters) - The U.N. Security Council delayed a key vote on Western Sahara as members haggled on Friday over a resolution seeking to kick-start negotiations over the disputed northwest African territory, diplomats said.

The Council had hoped to vote to renew the mandate of the 220-member United Nations peacekeeping force in Sahara, but also to call for U.N.-sponsored direct talks between Morocco and the Polisario independence movement.

But with Polisario unhappy with the draft resolution, diplomats from the 15 council members picked through its wording. The council now hoped to vote on Monday, when the peacekeeping force mandate expires, diplomats said.

Moves to resolve the long-standing dispute received a shot in the arm this month when both Morocco and the Polisario handed the United Nations proposals for the future of the desert territory of 260,000 people. That encouraged the Security Council to lend its support to talks.

Each side now says it is ready in principle to talk, but wide differences remain on the basis for negotiations over Sahara, which was annexed by Morocco after Spain abandoned its colonial occupation in 1975.

The territory, spanning an area larger than Britain, has lucrative phosphate reserves and rich fishing grounds. Many thousands of Sahrawis live in refugee camps across the border in Algeria, where Polisario is based.

Diplomats said a key sticking point in the text was how to refer to the rival proposals on Sahara's future. Polisario objects to wording praising Morocco's "serious and credible" efforts but merely "taking note of" the Polisario plan.

Washington has moved towards Morocco's position. Nearly 170 U.S. congressmen on Thursday urged President George W. Bush to embrace Rabat's proposal, saying the dispute impeded the fight against al Qaeda and other militant groups in North Africa.

Also backing Morocco in the Security Council is France. Polisario is supported by South Africa and some other developing countries.