WASHINGTON - Rep. Richard A. Gephardt of Missouri has decided to step down as leader of the House Democrats after Republicans scored decisive victories in the midterm elections.

An intense race to succeed Gephardt is already under way, with Rep. Nancy Pelosi of California, the No. 2 House Democrat, expected to seek his post in the face of stiff competition from Rep. Martin Frost of Texas.

If Pelosi prevails, Rep. Steny H. Hoyer of Southern Maryland would be in a strong position to replace her as party whip.

Both Gephardt and the Senate Democratic leader, Tom Daschle of South Dakota, have been pondering whether to run for president in 2004.

Gephardt, who aides say is to announce today his intention to step down next year, had been expected to relinquish his post after the elections.

Democratic Reps. Harold E. Ford Jr. of Kentucky and Peter Deutsch of Florida suggested yesterday that Gephardt should quit his leadership role, saying their party deserves an alternative to the 61-year-old who has led House Democrats for eight years.

Daschle, the Senate majority leader, will now become minority leader. He had put off any decisions about his future until after the midterm elections, a spokeswoman said, and has not signaled when he might announce his plans.