Despite forecasts of economic recession next year, the Gannett Co. expects advertising business to grow modestly for its group of newspapers around the country?ÛÓnumbering 78, the largest chain owned by any one publisher.</br></br>In addition, Gannett President Allen Neuharth is telling publishers of his company?Ûªs newspapers here this week that despite a commitment to follow President Carter?Ûªs wage and price guidelines, spending for news operations in 1979 will be boosted by 13 percent. .</br></br>?ÛÏWe?Ûªre going to put more money into the product (newspaper content) even if we have to scratch harder on the revenue side,?Û? Neuharth said in an interview yesterday.</br></br>-' Neuharth matfe his remarks during a break at a three-day meeting for all Gannett publishers and other top corporate officials?ÛÓabout 135 of them?ÛÓ that is being held at the Capital Hilton hotel.</br></br>Ironically, the Gannett meeting will continue into Thursday?ÛÓthe same day the Federal Trade Commission begins a controversial symposium on concentration of media ownership, in which