In case those $600 rebates (or 4.8% financing) fail to jumpstart sales of the new Taurus and Sable,is strongly encouraging employees at its regional marketing offices to think Taurus when they turn in their existing company cars. Ford executives and mid-level employees eligible for discounted leases also are getting a hint. That may trim inventories, which stood at a slightly higher than normal 72-days supply (Taurus) and 83-days supply (Sable) at the end of 1995. Ford is offering the $600 rebates or 4.8%, 48-month financing on 17 models. They're even discounting Bronco by $2,000. The only exceptions: the new F-series pickup and Explorer, which continues to ride high on the crest of the sport/utility wave.