Rep. Samuel E. Rohrer, R, Berks, is considering a bid for the Republican nomination for governor. Mr. Rohrer, an economic conservative first elected to the House in 1992, said he would make a final decision on the race within three weeks, and that it was "more likely than not, that he would go ahead with his candidacy. The Eastern Pennsylvania lawmaker would be the third contender in the GOP field, along with Attorney General Tom Corbett, and Rep. Jim Gerlach, a Chester County congressman. "I am a constitutional Republican, that's how I describe myself, he added.