IRKUTSK, U.S.S.R., AUG. 1 -- Secretary of State James A. Baker III and Soviet Foreign Minister Eduard Shevardnadze held a leisurely round of talks in this central Siberian city today to prepare for a summit meeting in Moscow, possibly at the end of this year, and to discuss arms control, economic issues and a formula for resolving the 12-year-old war in Afghanistan.

Shevardnadze, however, speaking to reporters before the talks started, dismissed widespread speculation that the two superpowers might agree soon on an election plan to end the Afghan conflict. "It would be difficult to reach a solution," Shevardnadze said, "because we cannot decide for the Afghans. But we can help, and I think in that regard, perhaps we will be able to help."

Washington and Moscow have narrowed their differences in recent months on procedures for holding elections to end the war, which is estimated to have left up to 1 million Afghans dead and another 5 million in refugee camps in Pakistan and Iran.

Speculation that an agreement was near was increased when President Najibullah, who heads the Soviet-installed government in Kabul, arrived in the Soviet Union on a surprise visit Sunday. Radio Kabul said the 43-year-old Najibullah would undergo unspecified "medical treatment" and was making the trip "at the invitation of the Soviet government."

Shevardnadze told reporters that Najibullah was "not in Moscow. He is on vacation," and that he had no doubt Najibullah would return to Kabul. Shevardnadze said Najibullah's visit "has no relation to our talks."

In Moscow, meanwhile, Afghan Ambassador Daud Razmyar met with Alexander Belonogov, a deputy foreign minister, to discuss "a political settlement in Afghanistan," according to the official Tass news agency.

Administration officials have been reviewing a proposal, floated informally a month ago by the Soviet ambassador to the United Nations. The proposal would allow Najibullah to remain in power during internationally accepted elections -- a key Soviet condition -- but would require him to give up key ministries to an interim governing group, meeting the U.S. demand that he not enjoy the full benefits of incumbency.

Baker, chatting briefly with reporters in the early afternoon, said he and Shevardnadze had discussed "matters affecting scheduling, some arms control work and some economics issues." Afghanistan would not be discussed until this evening or perhaps Thursday.

Asked if they would set a date for a summit meeting this year between President Bush and Soviet President Mikhail Gorbachev, Shevardnadze said the question had been discussed but "it is not the most important thing now to set the date. The important thing is to prepare the ground."

The ministers' meeting here, their 11th this year, was extremely slow-paced, as the two spent most of the day boating and fishing on idyllic, mile-deep Lake Baikal, the world's largest fresh-water lake with about 20 percent of the world's fresh-water supply.

Baker and Shevardnadze met for about three hours this morning. They spent the rest of the day riding a hydrofoil up the Angara River to the mouth of the lake and then fishing on a Soviet motorboat. The Soviet diplomat caught one fish and the American none.

Baker, asked by reporters what the two had discussed during the 90-minute hydrofoil trip, said, "We've been talking about Lake Baikal." He then related the history of the area and the construction of a railroad spur with numerous tunnels shortly before the Russo-Japanese War in 1905.