Katy Perry -- Post-Obama Dinner with My Conservative Parents

Just hours after havin' lunch with Michelle Obama ... and one day after stumping for the Pres at a Democratic rally ... Hollywood liberal Katy Perry sat down for a peaceful dinner with her ultra-conservative parents.

Katy has some major philosophical differences with her folks -- who are very devout pentecostal Christians ... especially when it comes to social issues like gay marriage.

But last night, they didn't let politics get in the way of a good meal ... and dined together at Red O in L.A. to celebrate Katy's 28th birthday.