After three weeks of handshakes, warm smiles and widely televised mutual admiration, Israeli Prime Minister Ehud Barak and Palestinian leader Yasser Arafat got down to the details of peacemaking today--and promptly encountered the reality of their disagreements.

In the longest and most substantive of their three meetings since Barak took office July 6, Arafat appeared to reject Barak's proposal that Israel postpone further handovers of West Bank land until the two sides move closer to a comprehensive agreement on the many issues that still divide them. As expected, Arafat responded that the Israeli pullback in question, already overdue by several months, should be carried out "immediately."

Arafat, who heads the Palestinian Authority in Gaza and the West Bank, also demanded the Israelis move ahead with other past commitments--releasing Palestinians imprisoned on security charges, allowing Palestinians free passage between Palestinian-controlled territories in the Gaza Strip and the West Bank and allowing construction of a harbor in Gaza. Arafat did agree, however, to authorize top aides to discuss the proposal for two weeks, starting Thursday, and then make recommendations. But his basic position seemed clear.

Between the two men, the atmosphere and smiles were still warm, the handshakes still two-handed. Aides to both leaders insisted no crisis was afoot. But as the two sides met at the Erez Crossing between Israel and the Gaza Strip, there was a sense that the tough going has begun.

On the Israeli side, Barak is apparently loath to proceed with phased territorial concessions, seeing them as squandering political capital while making it even more difficult to reach a breakthrough on tough issues like the future of Jerusalem, water and permanent borders--not to mention Palestinian statehood--that would have to be part of the final settlement both sides say they want.

With each incremental Israeli troop pullback, his aides say, Barak is certain to encounter a political uproar, not least from the 150,000 Jewish settlers in the West Bank, many of whom already feel threatened by the prospect of a receding Israeli security presence.

On the Palestinian side, however, Arafat is eager to show his restless people territorial gains after three years of inertia under Barak's predecessor, Binyamin Netanyahu. Although Barak is reported to be offering further concessions should the Palestinians agree to a postponement, analysts believe Arafat cannot wait.

The Israeli pullback in dispute was brokered by President Clinton and agreed to in marathon negotiations between Arafat and Netanyahu at Maryland's Wye River Plantation last fall. Under the Wye River Memorandum, Israel was to withdraw its troops from a further 13 percent of the West Bank. That would put about 40 percent of the West Bank partly or fully under Palestinian control.

The pullback began with a small Israeli redeployment in November and was to have been completed after two bigger phases by early spring. But Netanyahu, under political pressure from his hard-line allies, suspended the pullbacks in early December. He accused the Palestinians of failing to fulfill their end of the bargain: suppressing terrorist groups within their territories, seizing illegal weapons, trimming their police roster and halting hateful articles against Israel in the Palestinian press.

Barak reiterated his intention to implement the Wye agreement fully, and said he would make no change without Arafat's consent. He also said the Palestinians have to live up to their end of the agreement, especially on fighting terrorism. However, Barak stopped short of accusing them of failing to comply, as Netanyahu did.

Israel's intention, said Barak, is to pursue "the path of cooperation with the Palestinians, progressing with great momentum toward implementation of agreements and achieving a termination of conflict."

Arafat, who has cracked down on terrorist groups since last fall, promised to continue doing so. But he made his impatience with Israel plain. "We must see the accurate implementation of agreements signed on the basis of reciprocity," he said.