NATIONAL AUSTRALIA BANK LOWERS BENCHMARK PRIME National Australia Bank Ltd <NABA.S> said it lowered its benchmark prime lending rate to 18.25 pct from 18.5, effective today, but left its base rate at 18.5. The benchmark reduction brings the rate into line with the prime rates of most of Australia's trading banks, including those of two of the other three major trading banks. However, the rate is above the 18 pct - the lowest ruling rate - set by the other major, the Australia and New Zealand Banking Group Ltd <ANZA.S>, on Friday and effective today. The benchmark is based on short-term interest rate movements while the base rate is tied to longer-term trends.