A fragmentation warhead? Probably not very effective against ballistic missiles. The U.S. interceptors us kinetic energy (hard kill) capability.
Of course, the old Spartan system used a multi-megaton warhead, until Jimminy Carter shut it down.
“The Russian Federation has been promoting the defense capabilities of the S-300PMU [SA-10] in the foreign markets; and in 1994 admitted that the S-300PMU had low-spectrum capabilities ranging from defense against stealth aircraft and cruise missiles to ICBMs.
One variant has been credited with a 0.9 kill factor against ballistic-missiles.”
http://www.newsmax.com/articles/?a=2000/4/24/53247