Not very special effects.
Wow. This was a bit of a stinker. No chemistry btwn Newman and Andrews. The Soviets seem about as competent as Keystone cops most of the time. How about Newman's contact at the University tripping him so he falls down a flight of stairs! Great way to make contact--too bad if you break his neck!
The coupe de grace is the fakey, shakey rear-projection work. Almost funny.
Here's a pretty spot on review from that time:
http://www.nytimes.com/library/film/072866hitch-curtain-review.html