* Honda says won't use Takata front air bag inflators
* U.S. imposes fine of $70 mln, could be more
* Takata shares close down 13.4 pct, briefly down 20 pct
* Takata CEO says to phase out ammonium nitrate
(Recasts, adding more Honda comment, Toyota, Nissan, analyst.
Changes slug, pvs USA-TAKATA/)
By Naomi Tajitsu and David Morgan...More