AS Secretary of State James Baker III embarks tomorrow on his eighth trip to the Middle East since the end of the Gulf war, prospects for a long-sought Middle East peace conference appear brighter than ever."The chances look very good at this point," acknowledges one State Department official. "We're at the stage where it would be terribly damaging for any party to back out now," adds a Washington-based Israeli journalist. The major unresolved matter Mr. Baker will address in discussions in Syria, Israel, Egypt, and Jordan will be the makeup of a Palestinian delegation to the peace talks. Diplomatic observers here have been encouraged by the tacit agreement of the Palestine Liberation Organization (PLO) to the idea of forming a joint Jordanian-Palestinian delegation. The decision could pave the way for a United States-brokered formula that would allow the PLO to claim an indirect role in peace talks while bowing to Israel's adamant refusal to deal directly with the organization or with Palestinians living in East Jerusalem, which Israel claims as part of its capital. In Jerusalem Baker will encounter a spirited tactical debate that augurs less well for a peace settlement. Cool to the idea of peace talks in the first place, many members of the country's ruling Likud coalition are divided on whether Israel should back out now, before the conference convenes, or wait until after it begins and use the excuse of irreconcilable differences over such issues as trading land for peace to make a more graceful exit. It is now too late to exercise the first option, most observers agree. Even so, recent speeches by Israel's prime minister have been more adamant than usual. Diplomatic observers have also been concerned about alleged Israeli government news leaks that, some say, could be used to provide an excuse to torpedo the conference before it begins. Recent news stories have charged that the US has imposed new conditions for Israel's participation in peace talks. In fact, say several Israeli sources, there have been no "new" demands, merely clarifications by the US of its own position on issues like land-for-peace that would have to be included if the terms of Israel's own participation in peace talks are laid out in a formal memorandum of understanding between the two nations. "The leaks could provide a justification if the government decides it doesn't want to go to the conference," says a knowledgeable Israeli source in Washington. "They'll play it as an option. They'll wait for Baker and if they get the guarantees they're looking for, they'll go." Also difficult to finesse will be Israel's refusal to halt the construction of Jewish settlements in the occupied West Bank and Gaza Strip. No Arab state has chosen to use the settlements policy as an excuse to back out of the conference. But Arab leaders say without some change in the policy it will be difficult for the negotiations to progress very far. "Unless there is progress on this it will be difficult to start talking about water and the environment," says one Arab ambassador here, referring to plans to convene multilateral discussions on these and other issues as part of the peace process. Under a US proposal the process would begin with a one-time conference sponsored by the US and Soviet Union, followed by direct negotiations between Israel and its Arab neighbors. So far no venue for the talks has been designated, though various informed sources suggest that Lausanne, Switzerland, is high on the list of possibilities. The attraction of Lausanne for Baker is said to lie in the fact that it would replicate the restful Wyoming environment where he and former Soviet Foreign Minister Eduard Shevardnadze held productive talks two years ago. Another, still slim possibility, these sources speculate, is that President Bush may decide to launch the talks personally after participating in a NATO summit in Rome on Nov. 7 and 8.