ALTON, Ill. (AP) _ Terrence Brennan, editor of The Mercury in Pottstown, Pa., for the past three years, has been named publisher of The Telegraph.

The announcement was made Wednesday by C. Thomas Marschel, president of Suburban Newspapers of Greater St. Louis, parent company of The Telegraph.

Brennan, 41, replaces Bruce Spotleson.

Brennan became editor of The Mercury in September 1985 and helped guide the 30,000-circulation morning newspaper about 50 miles west of Philadelphia. For the three years before that, he served as assistant sports editor of the Delaware County Daily Times, a 60,000-circulation newspaper in suburban Philadelphia.

Brennan also worked as a sports writer for the Philadelphia Bulletin from 1975 until the paper closed in 1982. He is a 1968 graduate of Penn State University.

''This paper belongs to the people of Alton,'' said Brennan, promising to keep The Telegraph's focus on the local community. ''They've grown up with it. It's a part of their heritage, a part of their family, and it belongs to them.''