your post prompted me to do a little looking myself... and from i can garnish, there's no specific security agreement that commits the united states. it's a "commitment" by the u.s. that began as far back as the '60's, and was first explicitly voiced by reagan, and every president since. it's a long standing de facto "commitment to maintain israel's qualitative military edge against all its potential adversaries. you can't find a link to the agreement because there is no specific agreement...and there's certainly no stated degree to which that "edge" needs be maintained. and personally, i think it's an unwise "commitment" for the u.s. to make to ANY country.
from the article: 'Bush sold Arab states arms in violation of deal with Israel'