State Sen. Gib E. Armstrong, who chairs the Appropriations Committee and has served in the Legislature for more than 30 years, plans to retire at the end of next year and not seek a sixth term in the Senate.

Armstrong, R-Lancaster, said he wanted to retire eight years ago, but instead stayed on to help push through a convention center project now under construction in downtown Lancaster.

Armstrong, who was elected chairman of the Appropriations Committee last year, said the strain of the leadership position played a role in his decision.

‘‘I’m not going, to prove a point, to put my family through four more years of long hours,’‘ said Armstrong, who notified supporters of the decision Saturday. Armstrong and his wife, Marti, live on a farm in Refton. They have three sons and a daughter and seven grandchildren.