This weekend's race in Austin, Texas is the first time that the sport has returned to the USA since 2007.
"I've done more interviews for this race than I can remember and that's a great thing," BBC Sport quotes the 72-year-old American as saying. "Let's face it, we're saying Formula 1 needs America and America needs Formula 1. I think it's both. It's a win-win situation.
"The majority of the sponsors there are in Formula 1 are global companies that do a lot of business in the United States, so to have the exposure in this big market here is what's needed. This is a good thing.
"They probably don't realise that there is a fanbase. That has been understated grossly in my opinion and I think that's what we're going to find out. We can look forward to this next year and then the following year and the following year. There has to be stability and then you'll see the fanbase is for real."
Andretti won the world championship in 1978.