NET ASSETS OF SOC SEC CONTINUE TO RISE BEYOND 2020 WON'T SEE SOC SEC DEFICIT OUT TO 2020,PERHAPS LATER OUTLOOK FOR SOC SEC 'ALL RESTS ON PRODUCTIVITY' SOC SEC SHORTFALLS'NOW SUBJECT TO CONSID QUESTION' SOC SEC SHORTFALLS NOW MAY NOT BE INEVITABLE INTEREST ON SOC SEC SURPLUS MAY OFFSET HIGHER COSTS