Please tell me which zoos in the United States have an exhibit of
white bengal tigers?

Richmod Zoo, Richmond Virginia has one. (located in Chesterfield county VA)

This article may be of interest:

http://www.felineconservation.org/R3/Husbandry/Cats/whitetiger1.html

Busch Gardens in Tampa, Florida has white tigers.

I did a quick search for you and found this website
http://www.cranes.org/White_Tiger.htm which has proved to be
interesting reading for me. The article talks about the White Tiger
and its history, its worldwide numbers broken down into different
areas and some of the controversy that surrounds the white tigers.

Some US zoos with white tiger exhibits include:- 

Knoxville TN "Knoxville Zoo currently has five tigers, representing
three of the world?s five tiger species. There are three Bengal
tigers, two of which are white, and one each of Amur and Indochinese
tigers at Knoxville Zoo" (http://www.knoxville-zoo.org/078.htm)

Sacramento Zoo (CA) (http://www.saczoo.com/) has two white tigers.

As well as Busch Gardens, FL (http://www.buschgardens.com)as the
previous poster mentioned.

I hope this has been of some help!

The Toronto Zoo has a couple of white bengel tigers.  Are you planning
on visiting an exhibit?  Of Course Toronto is in CANADA but if you
live close to the border you should be able to visit.