UNITED NATIONS -- U.N. Secretary-General Kofi Annan appealed to a deeply divided Security Council on Tuesday to find common ground on Iraq, saying he is optimistic of an agreement. But some council members said they weren't so hopeful.

The United States has been pressing for a vote next week on a resolution to give U.N. backing for a war, though it doesn't currently have the nine "yes" votes needed. White House spokesman Ari Fleischer said Tuesday the vote was "desirable" but "not necessary," leaving open the possibility that the United States would not call for one.

U.S. Ambassador John Negroponte, asked if the United States would withdraw the resolution if it didn't have enough votes, said: "We believe that support should be there and we're not facing that kind of situation," he said. "I think we'll cross that bridge if and when we come to it, but we don't think we should have to come to that point."

But Annan's appeal and the possible change in U.S. tactics reflect the polarization in the Security Council that appears to have hardened in recent days. Many undecided council members have called for a compromise among the key powers -- but the two camps are so far apart that diplomats said there have been no substantive talks.

With top weapons inspectors Hans Blix and Mohamed ElBaradei to report Friday on Iraq's cooperation, Annan called on the council to unite, as it did last November in unanimously adopting a resolution that gave Iraq a final opportunity to disarm or face serious consequences.

'I am optimistic'

"The members have different positions, and of course, I hope through the discussions and the exchange of views they might be able to find some common ground to move forward," Annan said at a private luncheon with the 15 Security Council ambassadors.

Asked whether he was optimistic that this might happen, Annan replied: "I am optimistic."

But other council members were less hopeful of resolving the council split that has left the United States, Britain and Spain supporting authorization for war but France, Russia, Germany and China backing inspections at least into July.

"Everybody talks about compromise but I can't see one," said Bulgaria's U.N. ambassador, Stefan Tafrov. "I'm afraid that positions have hardened instead of coming closer, and it's harder now to achieve the unity of the council."

"We need some kind of movement to achieve the unity of the council, which is the objective of Bulgaria," he said.

U.S. officials have said they would be open to suggestions on their resolution but would not negotiate the substance of it. If the council rejects the U.S.-backed draft, Bush has said he is prepared to fight with a coalition of willing nations.

Nonetheless, Annan said he believes that there are "serious discussions" going on.

Earlier, he declared that war must be a last resort and called Iraq's destruction of Al Samoud 2 missiles "a positive development."