Pryce, 56, was her party's fourth-ranking leader before the GOP lost control in the 2006 election. She narrowly survived a challenge last fall from Democrat Mary Jo Kilroy.

Kilroy, a Franklin County commissioner, is running again in 2008, an election in which Democratic hopes run high because of voter disenchantment with President Bush and the Iraq war.

Democrats says they also will compete strongly for the seats being vacated by former Speaker Dennis Hastert and seven-term Rep. Ray LaHood, both of Illinois.

Top Republican officials in Ohio and Washington said she plans to step down when her term ends next year.

One of the officials said the decision was largely a family matter for Pryce, the single parent of an adopted child.

With Pryce's and Hastert's departures, only one of the top four House Republican leaders from the GOP-controlled 109th Congress appears likely to seek election next year: Roy Blunt of Missouri, the GOP whip. Former Majority Leader Tom DeLay, R-Texas, stepped down last year.

Even before Pryce's plans became known, Democrats saw her Columbus-based district as among the most competitive held by a Republican. An open seat will be even more difficult for Republicans to defend, but party activists say they will do so, arguing that Democrats already failed once -- in 2006 -- when many factors were in their favor.

Doug Thornell, a spokesman for the Democratic Congressional Campaign Committee, said: "Mary Jo Kilroy came within 1,055 votes of winning last cycle, and we expect this race to provide us with a tremendous opportunity to strengthen our majority."