HARRISBURG — In a Legislature whose first year was most memorable for the number of stalemates it spawned on major issues, at least 18 representatives and senators are not seeking re-election this year.

That is far fewer than the 31 lawmakers who vacated their seats in 2006 — the first election year after the government pay-raise scandal that rocked the state's political establishment — when voters also ousted 24 incumbents running for additional terms.

This year's number of expected open seats is closer to the norm, as are the reasons the departing legislators give for their decisions to step down when this Legislature goes out of business on Nov. 30.

A desire to move on, to do something else, is the most common explanation. At least two of the departing House members — Steven Cappelli, R-Lycoming, and Daylin Leach, D-Montgomery — plan to run for the Senate. But frustration and fatigue are cited too.

"I just couldn't bring myself to run another campaign," said Rep. David Steil, R-Bucks. "I was just burned out."

Steil, who co-chaired Speaker Dennis O'Brien's Legislative Reform Commission, said he also is discouraged that the Legislature lacks the appetite to go beyond simple changes in its operating rules and tackle reforms on more politically charged subjects such as campaign financing and redistricting.

"It isn't possible in another one or two terms," said Steil, 65, who owns a company that manufactures electronic instruments for environmental monitoring.

Rep. Lisa Bennington, one of the 55 freshmen legislators elected in the anti-incumbent sweep of 2006, plans to leave after only one term because she says changing Pennsylvania's laws simply takes too long.

Bennington, D-Allegheny, says she was discouraged by the lack of progress last year on gun control, banning smoking in public places and a proposal to require hospitals to provide sexual assault victims with emergency contraception. She plans to resume her full-time practice as a divorce lawyer in Pittsburgh.

"Coming from the private sector," she said, "I really am used to deadlines and timelines and work hours that are pretty much defined by the sun."

The four senators who plan to step down include Gib Armstrong, R-Lancaster, and Gerald J. LaValle, D-Beaver — the chairman and ranking Democrat on the powerful Appropriations Committee.

More incumbents still may announce plans to retire, since legislative candidates cannot begin circulating their nomination petitions until Jan 22. They will have three weeks to gather enough signatures to qualify for the April 22 primary ballot.

Already, with 10 Republican seats and eight Democratic seats expected to be open, campaign strategists for both parties are busy constructing scenarios to strengthen their presence — especially in the House, where Democrats hold a one-seat majority.