The economy will slow considerably next year...

The economy will slow considerably next year and will probably tumble into a recession by 1990 at the latest, according to a survey by the National Assn. of Business Economists. The average forecast of 66 economists polled last month is for inflation-adjusted gross national product growth of 2.5% in 1989. Although that is slightly higher than the 2.3% projected by the group in September, it is still well below the 3.8% growth that the economists expect this year. Consumer prices are likely to rise 5% in 1989 after a projected 4.1% increase this year.