President Bush said Friday there is "real cause for optimism" about convening a Mideast peace conference and pledged to keep trying despite hard-line differences between Israel and Syria.

A tired-looking Secretary of State James A. Baker III met with Bush over lunch to report on his fourth Middle East mission in two months and to discuss options for the future.Later, during an exchange with reporters, Bush brushed aside speculation that he might invite Arab and Israeli leaders to Washington to see if the deadlock could be broken. "That's a detail I'm not discussing," he said.

The president said he would send Baker back to the Middle East "if there's reason to go back." Baker has flown 67,563 miles in the four rounds of shuttle diplomacy; Bush joked that another trip "might kill him."

An administration official said that there are no plans for Baker to make another trip and that the next step is to await responses on issues Baker left with the parties.

Despite Bush's optimism, the official, who requested anonymity, said the president wanted to convey "a sense of reality that this is a long-term process. It won't be settled overnight."

The president and the secretary appeared determined to put the best face on developments despite apparent obstacles.

"My assessment after hearing the report from Secretary Baker is that there is real cause for optimism," Bush said.

"And we will continue to work this process," the president said. "We're not about to stop. . . .And when you're working a problem this complicated, you just keep on plugging away."

Like Baker, Bush refused to discuss any proposals put forward by the United States, saying that quiet diplomacy was in order.