A senior U.S. official said yesterday that the Reagan administration wants the Soviet Union to withdraw from Afghanistan "before the end of next year," and a high-level adviser to Soviet leader Mikhail Gorbachev said it is his "personal point of view" that this will happen.

In separate pre-summit briefings here, U.S. and Soviet officials otherwise offered widely different views on a political settlement in Afghanistan, indicating that the two superpowers are still far from an understanding.

Gorbachev and President Reagan have said they intend to discuss the Afghan conflict at the summit next week, and Reagan has said he will ask Gorbachev to set "a date certain" for a Soviet pullout.

Meanwhile, Soviet officials have been hinting that Gorbachev will tell Reagan that the 115,000 Soviet troops stationed there could be withdrawn within 12 months if the United States agrees to halt military support for the Afghan resistance.

U.N. mediator Diego Cordovez, who has been conducting "proximity talks" between Pakistan and Afghanistan in Geneva on a political settlement, held a secret meeting there yesterday with diplomats from the two neighboring countries in a bid to break the deadlock on a withdrawal timetable.

No progress was made in bridging the gap, according to a source close to the talks, Washington Post special correspondent John Parry reported from Geneva.

"I think they were trying to put together some kind of compromise deal which Reagan and Gorbachev could have rubber-stamped at the summit next week. But nobody is ready for that yet," a Pakistani diplomat told Parry.

In its last offer to Cordovez in September, the Soviet-dominated Kabul government suggested 18 months until withdrawal, while Pakistan had proposed eight. Last Monday, Afghan President Najibullah publicly proposed a 12-month timetable, an offer apparently not repeated to Cordovez yesterday.

Speaking here yesterday, Yevgeny M. Primakov, a senior adviser to Gorbachev on Afghanistan, detailed the Soviet view of a political settlement, saying, "I believe Soviet forces will be withdrawn next year. This is my personal view."

Primakov, director of the Moscow Institute of World Economy and International Relations, said Najibullah's "mechanism" to bring about "national reconciliation" with rebels "is working out . . . maybe not quite well, but it's working."

Primakov said Najibullah is offering to establish a multiparty "coalition government," in which rebels would gain the post of prime minister and half the Cabinet seats. He gave no indication that Najibullah is ready to cede control of the armed forces or such other key posts as the interior or foreign ministries.

Primakov said that a "stable cease-fire" exists in many areas of Afghanistan and that Soviet troops have been withdrawn from 12 of the 30 provinces.

Primakov suggested that, if the United States declared a one-year "moratorium" on aid to the resistance so as "not to overburden the {Soviet} load," then "during this one year, we will pull out our forces."

Three senior administration officials briefing reporters on regional superpower conflicts made clear that the United States will not accept the Soviet notion of a "coalition government" dominated by the Afghan Communist Party.

One official said the Soviet demand for an end to U.S. aid is "a red herring" because the administration has agreed that, as a guarantor of a U.N.-sponsored political settlement, "that stops . . . . The issue is a Soviet withdrawal and a commitment to withdrawal."

"We are asking for a short timetable, but we want to know a date certain for it to begin and end. I think we would also like to see that ending date before the end of next year," he said.