G.O.P. Glum as It Struggles to Hold Congress

The battle for Congress rolled into a climactic final weekend with Republican Party leaders saying the best outcome they could foresee was losing 12 seats in the House. But they were increasingly steeling themselves for the loss of at least 15 seats and therefore control of the House for the first time in 12 years.

Democrats and Republicans said the battle over the Senate had grown fluid going into the final hours before the elections on Tuesday. Democrats said they thought they were almost certain to gain four or five seats and still had a shot at the six they need to take control.

Republicans were pouring money into Senate races in Michigan and Maryland this weekend to take advantage of what they described as last-minute opportunities, however slight, in states currently held by Democrats. And a new poll Saturday showed that Senator Conrad Burns, the Montana Republican, was tied with his challenger after a visit there by President Bush.

Party strategists on both sides, speaking in interviews after they had finished conducting their last polls and making their final purchases of television time, said they were running advertisements in more than 50 Congressional districts this weekend, far more than anyone thought would be in play at this stage.