The economy will move into recession early in 1980, but businesses and consumers will not get the usual benefits of an economic slowdown such as lower interest rates and lessened inflation.

Instead, inflation will be worse than in 1979 and the prime interest rate, which just fell to 15 1/4 percent from 15 3/4 percent, will rise again to the 16 to 17 percent range.

That is the gloomy assessment of Henry Kaufman, chief economist of the investment banking firm Salomon Brothers, one of the more accurate prognosticators of the record interest rate levels that haver occurred in 1979. p

Kaufman said the long-awaited recession will begin in earnest during the first half of 1980 and will not end until sometime in early 1981.

At the same time, he said, inflation will accelerate because of higher wage settlements, continuing increases in oil and other energy costs, and because declining output of goods and services will make already flagging productivity increases even harder to achieve.

The inflation rate, as measured by the so-called gross national product deflator, will be in the 10 to 11 percent range next year, compared with about 9 percent this year. Other measures of inflation -- such as the consumer price index -- are rising faster than the GNP deflator, in part because the deflator is a broader measure of price changes.

Despite the recession, with its attendant increase in unemployment, wage settlements will average between 9 and 11 percent in 1980, as workers try to compensate for the damage done to their pocketbooks this year and in anticipation of future inflation.

In part because of rising inflation -- and in part because business spending will remain high during the first half of 1980 and because consumer spending also will remain strong until unemployment becomes widespread in the spring and summer -- credit demands will be high.

In the 1974-75 recession, Kaufman noted, private credit demands fell 45 percent, from $138 billion to $80 billion. Next year he predicts only a 15 percent decline in private credit demands.

At the same time, he said, the federal budget deficit will grow from about $30 billion to $50 billion.

Strong credit demands, coupled with a need for a continued tight monetary policy on the part of the Federal Reserve, will prevent interest rates from falling as far and as fast as they did in earlier recessions. Interest rates will not begin to decline until after mid-year, he said.

He said that short-term interest rates, such as the bank prime rate (the interest charged top-rate business borrowers for short-term loans) will climb to between 16 and 17 percent. Treasury bill rates, which reached a record 12 percent level a couple of weeks ago, will move to about 13 percent. Top-grade utility bond rates, now at a record 12 percent, will hit 13 to 13 1/2 percent.

Not all analysts share Kaufman's view. Many think that the decline in prime rates which started two weeks ago signals that the peak in interest rates has been reached and that rates should continue to decline, although more slowly than in prior economic slowdowns.

Kaufman said that interest rates "never head in one direction steadily" and that recent declines were merely temporary.

He predicted a record increase of $39.5 billion in corporate bond issues by U.S. companies in 1980.