"The Senate's a top priority, and you'll see a tremendous amount of resources garnered to protect the majority there," says one G.O.P. strategist familiar with the party's planning. Says a Democratic strategist, "More attention than ever is being directed to the Senate races."

In what it is privately calling it's "firewall" strategy, the Republican National Committee has recently spent close to $4 million in three crucial Senate races — Ohio, Missouri and Tennessee — in the hope of holding Democratic gains to a maximum of five seats. No new RNC money has gone to House races during that time.

At the start of the fall campaign, national Republican leaders developed a strategy to pour most of the national money into three states — Ohio, Tennessee and Missouri — to create a firewall against a Democratic takeover. One Republican Party official said Mr. DeWine’s continued problems in Ohio had convinced them to in effect rebuild a firewall that has now partly collapsed, and to find a state to replace it.

The decision about Mr. DeWine’s seat came after recent internal polls showed Mr. DeWine’s Democratic challenger, Representative Brown, jumping to a large lead. Mr. Brown’s surge came despite a barrage of Republican advertisements intended to portray him as weak on national security — the very line of attack that had given party officials confidence earlier this year that Mr. DeWine would be re-elected.

Normally, a party would be averse to scaling back its help for senator in a state with as many as five competitive Congressional races also on the ballot. But in this case, Ohio Republicans said, Mr. DeWine and Republican Congressional candidates face the added problem of being dragged down this November by the party’s candidate for governor, J. Kenneth Blackwell, who polls show is facing a double-digit loss to the Democrat, Representative Ted Strickland.