The country is experiencing a peak of inflation now and the economy soon will start a gradual slowdown, according to the man behind much of E.F. Hutton's market analysis.

Newton Zinder, Hutton's first vice president and stock market analyst, said in an interview yesterday that by year's end inflation will have averaged about 9 percent, as compared to Carter Administration projections of 7.4 percent and Treasury Secretary W. Michael Blumenthal's recent revision to 8.5 percent.

Blumenthal conceded last week that the administration "screwed up" in its forecasting and that the rate could possibly go higher than his 8.5 percent prediction.

Blumenthal also said the administration now sees signs of a slowdown in the economy and that prices would moderate sometime this fall.

"We think we're seeing the peak of inflation now and economy has started to slow down and will continued to slow down and there will be a decline in the inflation rate," Zinder said yesterday. "We're seeing the peak of food inflation. Some (high food prices) resulted from severe winter.

"We're sort of doing a soft landing scenario," Zinder said. "The last two quarters of this year could see negative growth . . . by a relatively small margin."

When they look back next year, Zinder said, economists will say that the peak of inflation may have been during the first three or four months of 1979.

Zinder, the man who does the talking for Hutton, said that President Carter, in combating the nation's economic woes, "is trying to move in the right direction. There's less of the free-spending attitude we saw a few years ago."

Zinder also said the country is close to a peak in interest rates, although rates "may go up a little in a few weeks."

Predictions about the stock market, however, are not that easy for Zinder, who was here to attend a receptiion last night that marked his firm's recent expansion in the D.C. area.

"Right now the stock market is having a number of confusing and uncertain factors to contend with," Zinder said. "This often occurs in a turning point in the economy."

The confusion among the economists is adding to the market's chaos, Zinder said. ". . . the market reflects this confusion," Zinder added.

During the last decade, stocks have not been a good inflation hedge. But now, they represent such an opportunity, he asserted.

For the long term, Zinder said the country will experience "a period of relatively slow growth, slower than in the last few years." CAPTION: Picture, NEWTON ZINDER . . . sees stocks as hedge