Michael picked up on this report on Santorum’s early political career (the article’s title is at the top of this post):

They [the authors of the story] found a December 1995 interview with Philadelphia Magazine where Santorum admitted he had been basically pro-choice until he got into politics.

Elsewhere in the original 1995 article, it describes Santorum’s evolving politics:

He has forgone a past that was unexaminedly moderate for a platform that is unexaminedly conservative, including reversing, rather quietly, his pro-choice stance on abortion.

Another anecdote about Santorum’s earlier involvement in Republican politics confirms this picture:

It was the dawn of the 1980s, and the Reagan Revolution was stirring. But Santorum was not yet politically impassioned, and what political orientation he did have was quite moderate. “There was a Youth for Reagan group on campus, but Rick shunned them,” remembers a friend who was active with him in the Pennsylvania College Republican organization. “He always described them as right-wing fringe. But I don’t think he gave it much thought. Through three years in the College Republicans with Rick, I never heard him actually discuss issues.”

It makes it a little easier to understand why Santorum wouldn’t have had too much difficulty endorsing Arlen Specter’s presidential bid in the same year.