Movie set in pre-WW2 US. Involves a spy trying to escape from the US from a remote house near Canada. The Spy was a well-known public figure with some (If I recall) hidden German sympathies. The character was supposedly modeled after a real US pro-German public figure.

I think it was also produced in the early 1940s but I can't e certain.

Also starred a man and woman who thwarted (I think) the plot. They also developed something of a love interest but I don't recall that being very important.

Most of the action took place in a midcentury home located next to a large open field that served as the runway for the escape plane.

Eye of the Needle with Donald Sutherland? Just a stab.

Just a stab? Very good ;-)

But not a match, thanks. It was a great little movie but not what I was thinking of.

The real person that the Nazi sympathizer was modeled after might have been Charles Lindbergh, who was notoriously pro-Nazi. Lindbergh and a group of other prominent Americans were speaking out in favor of Hitler, trying to avoid war out of self-interest.