I have a recipe for an asparagus/pasta dish with a goat cheese sauce, Can I substitute Feta?
Probably not.

Goat cheese is a creamy cheese that melts well and makes a great sauce. Feta, on the other hand, does not melt. It will soften some, but still remain crumbly and chunky. The flavor is significantly different as well; it's much harsher.

You'd be better off with a fromage blanc, but chances are if you can find that in the US you'd be able to get the goat cheese there too. A common and more accessible substitute for goat cheese is cream cheese.