GENEVA, SEPT. 7 -- Pakistan and Afghanistan began a new round of U.N.-sponsored talks on a timetable for withdrawal of Soviet troops from Afghanistan today, amid cautious optimism that some kind of deal might be in the offing.

But Pakistani sources said that even if a deal is struck on a reported new Soviet offer to pull Moscow's 115,000 troops out of Afghanistan, problems would remain over the composition of a transition government that would replace the communist regime in Kabul.

These complications, they said, could prevent any agreement before next week's scheduled meeting between Secretary of State George P. Shultz and Soviet Foreign Minister Eduard Shevardnadze.

Diego Cordovez, the U.N. mediator who conducts the "proximity talks" -- so named because the two sides do not meet directly but have their points of view carried back and forth by Cordovez through a 100-yard-long corridor in the U.N. building here -- appeared to agree.

"It is interesting that the Afghans want to talk again, but I do not believe we are going to get a final agreement in these three days," he said in New York after the Afghan government had formally requested that the talks be resumed.

Afghan Foreign Minister Abdul Wakil was equally vague when he entered the first meeting today. "It's far too early to say," he told reporters when asked whether he thought an agreement was possible this week. The talks are scheduled to end Wednesday.

Afghanistan has proposed that the Soviet troops stay on for 18 months after the U.N. peace plan is signed. Pakistan has said the troops must leave within seven months. Moscow reportedly may try to break the deadlock by offering to withdraw its troops in a year.