THE conference that convened in Madrid Oct. 30 was a magnificent achievement for America's Middle East diplomacy. For the first time Israelis are sitting across a negotiating table from Syrians and Palestinians (the Israelis have been talking secretly with the Jordanians for decades). The Middle East peace train, stalled for more than a decade, is back on track and gathering steam. So isn't agreement, eventually, all but inevitable? If you believe in miracles, maybe.One very important reason that agreement is anything but inevitable is the manner in which the negotiations have been programmed. The Bush administration has reached into its bag of tricks and pulled out the idea of Israel and the Palestinians sitting down to negotiate over autonomy for the West Bank and Gaza. Now, proposals for autonomy have been ricocheting around ever since Israel occupied the West Bank and Gaza in 1967. The idea was resurrected at Camp David in 1978 when Egypt's Anwar Sadat insisted that Israel get out of these two areas and Israeli Prime Minister Menachim Begin refused. Autonomy seemed a fine compromise between the Israeli and Palestinian visions for the occupied areas. The Americans and the Egyptians looked on it as a kind of slow-acting pill to be served up to the Israelis: Take it now and you won't feel pain until years later, when the autonomy period ends. Mr. Begin regarded it as a placebo. He would swallow it if that was what was needed to get a peace treaty with Egypt, but only to show that he was a good fellow and ready to play along. He didn't expect it to affe ct his refusal to part with these areas. The problem with autonomy is that it looks simple but in fact is excruciatingly complex. The simplicity is in the broad outlines. The Palestinians take over running their internal affairs while Israel retains responsibility for defense and some elements of security, and for foreign affairs and economic policy. The Palestinians show themselves to be good and responsible neighbors and at the end of the predetermined autonomy period negotiate an amicable separation from Israel. Very fine. But peer under this shiny stone and you will discover a teeming multitude of angry little issues, any one of whose bite will be enough to poison the negotiations. How is the autonomous Palestinian government to be chosen? If elected, how will the electoral districts be drawn? Who will be allowed to vote - Palestinians from outside the West Bank and Gaza, those who have records of security offenses, Israeli settlers? And how much power will the autonomous government have? Will Prime Minister Yitzhak Shamir's negotiators - he has chosen a fearsome bunch of diplomatic toughs - agree to grant "Palestine" full authority even over garbage disposal? Once agreement is reached, how will it be possible to assure that its terms are respected? What will be the status of Israelis settlements and settlers? Will Israel stop putting up new settlements and stop expanding existing ones? The list of issues made to order for deadlock goes on and on. Autonomy is just the kind of broken terrain that an army wanting to fight an endless delaying action would select for itself. That is why it appeals so to Shamir and his associates. IN making autonomy the centerpiece of their Middle East diplomatic effort, President Bush and Secretary of State Baker have ignored a prime rule of problem solving: To overcome a truly difficult obstacle, you need a simple, practical plan. The simple answer, of course, is to remove the areas of the West Bank heavily inhabited by Arabs away from Israeli authority and join them in some form of association with Jordan, under closely monitored demilitarization arrangements that will assure Israeli security. But, one objects, Mr. Shamir won't negotiate about such an arrangement. That brings us to a critical point. To get Israel's Likud government to make any kind of meaningful concession in regard to the West Bank and Gaza, the Bush administration eventually is going to have to go to the mat with Shamir. The president and the secretary of state wouldn't dream of admitting this, but they knew it very well. A few months or even a few weeks ago, when the president was still riding high in the polls, a tussle with Israel's American backers must not have seemed such a daunting prospect. Bush in fact won a first round in September when he forced Israel, and the Israeli lobby, to back off its demand for immediate approval of $10 billion in housing loan guarantees. All summer long prospective Democratic presiden tial candidates scurried for cover, so futile did the prospect of defeating George Bush look. But with a weak US economy threatening to send his popularity plummeting, things are different. The Arab-Israeli dispute has never been close to Bush's heart. It is not likely that he will want to risk his chances for a second term just to push it a little nearer to solution. Talking about autonomy may be a good way to pass the time until the US presidential election is over. Ultimately, however, the delegates who assembled in Madrid will find autonomy too dauntingly complex to be negotiable, or if negotiated, workable. If they want to succeed they are going to have to look for other solutions.