For the first time in almost four years, Israeli and Syrian officials today began reckoning with the concrete implications of peace, sitting down with American mediators to hash out security arrangements and the potential for normal diplomatic and trade relations.

The convening of so-called technical committees marked the substantive beginning of the Shepherdstown talks, which opened here Monday amid soaring hopes for an end to half a century of bloodshed and confrontation.

In keeping with participants' vows of secrecy, State Department spokesman James P. Rubin declined to provide any details of today's discussions at the Clarion Hotel and Conference Center, except to describe them as "constructive, businesslike and positive."

Later in the day, however, Rubin hinted at frustration, telling reporters that the discussions thus far "have not expanded in any substantial way our areas of agreement" and that Secretary of State Madeleine K. Albright would recommend to President Clinton that he return here Thursday to nudge the talks along.

"In order to move from the chugging-along phase to the faster track we're going to have to get more new ideas," Rubin said.

The beginning of the technical meetings followed a social gathering here Tuesday night hosted by President Clinton, who held forth on the Civil War landmarks--including the Antietam battlefield--that surround this quaint West Virginia town and the history lessons they offer. Israeli Prime Minister Ehud Barak addressed the Syrian delegation, led by Foreign Minister Farouk Charaa, in Arabic as the guests sipped non-alcoholic beverages, according to Rubin.

Besides the committee meetings, Albright, who plans to be here throughout the open-ended talks, had lunch today with Barak and later sat down for an hour with Charaa.

The talks had gotten off to a bumpy start Monday when Syrian and Israeli officials clashed over Charaa's insistence that the two sides deal first with Israel's willingness to withdraw fully from the Golan Heights, the strategic plateau captured by Israel in 1967. Israeli officials countered that they could not consider the border issue without receiving Syrian assurances on security arrangements, water rights and the normalization of relations. Under pressure from Clinton and Albright, the two sides agreed to form four committees that would begin grappling with the main issues more or less simultaneously.

Besides the two committees that began meeting today on security arrangements and the nature of future relations, the others will focus on water issues and the extent of an Israeli withdrawal from the Golan.

As a gesture to the Syrians, U.S. mediators Tuesday night discussed the border issue with Syrian military officers, led by Gen. Ibrahim Omar, in what Rubin described as an informal session. Informal discussions on border and water issues--the two are closely related--continued today, Rubin said.

Someone who is in daily contact with the Syrian delegation said the American willingness to discuss the border issue now, even on an informal basis, was important to the Syrians as a "face-saving formula."

Also today, a Pentagon official confirmed Israeli press reports that Barak has asked Clinton for a military aid package worth $17 billion in the event that Israel pulls out of the Golan. According to a detailed account in the Israeli newspaper Ha'aretz, which the Pentagon official described as basically accurate, Barak has requested some of the most sophisticated weapons in the American arsenal, including Tomahawk cruise missiles, Apache helicopters and AWACS radar planes. The Israelis also have asked for a ground station that would provide real-time data on Syrian tank movements from U.S. spy satellites.

"It's a shoot-for-the-moon wish list," the Pentagon official said, adding that the Israeli request is already being disparaged by some U.S. military officials as "peace on our dime."

Though styling themselves as mere "facilitators," Americans have been intimately involved in every stage of the Shepherdstown talks. Those assigned to the security committee, for example, include Albright's military adviser, Gen. Donald R. Kerrick; Frank Kramer, an assistant secretary of state; and Bruce Riedel, the senior Middle East specialist on the National Security Council. The committee on the nature of relations between the two countries includes Martin Indyk, soon to take up his new post as U.S. ambassador to Israel.

The name of Indyk's group is revealing. Syrian officials insisted on calling it the committee on "normal peaceful relations," as opposed to "normalization," because they associate the latter term with Israel's peace treaties with Egypt and Jordan--settlements they regard as dishonorable. Normalization, in fact, is such a distasteful concept in Syria that Syrian journalists today complained to U.S. officials about the presence of a Jerusalem Post reporter at their work table in the press center at Shepherd College here.

The officials, who had intended to seat Israeli and Syrian journalists at separate tables, sheepishly asked the reporter to move.

Staff writer Thomas E. Ricks contributed to this report.