Democratic officials are bracing themselves for an ``October surprise'' -- possibly a Soviet grain deal -- to bolster Republican campaign prospects for the Congress. Rep. Tony Coelho of California, chairman of the Democratic Congressional Campaign Committee, says he doubts that President Reagan would have agreed to this weekend's summit in Iceland unless he were sure the meeting would be a political plus.
Both Republican and Democratic strategists say that the GOP's greatest problems in House and Senate races this fall are in the Midwestern farm belt.
Overall, Democrats are expected to pick up about 10 to 15 House seats, many of them in the Midwest. Democratic prospects have also been brightening in Senate races in North Dakota, South Dakota, Wisconsin, and Missouri. Mr. Coelho told reporters at a breakfast meeting on Thursday that, to be effective, a grain pact must be a multi-year deal that would get America's farm export pipeline flowing again.
Democrats clearly are concerned about the possible political impact of the summit, which comes only three weeks before Election Day. A major breakthrough on agricultural trade, arms -- or both -- could threaten Democrats' hopes for taking over the Senate and enlarging their control of the House, where they now enjoy a 253-to-182 margin.
Coelho, by raising the prospect of a grain deal with the Soviets, may be ``setting up'' the President for criticism if Mr. Reagan comes away empty-handed from his meeting with Soviet leader Mikhail S. Gorbachev.