Domestic automakers significantly increased their new car sales in the first 10 days of April, but industry analysts and officials say the sales boost does not yet constitute a real recovery.

New car sales for all five companies producing cars in the United States were 157,875 units, a 17.7 percent increase over the 134,102 cars sold in early April 1982.

The increase works out to a seasonally adjusted annual sales rate of 6.4 million cars, 32.5 percent better than the year-ago rate.

Industry analysts and company officials said the new 10-day figures are good mostly because the sales numbers from the year-ago period were so bad.

"Last year was terrible. We had a real air pocket in sales," said David Healy, an analyst with New York-based Drexel Burnham Lambert. "I'd love to say that this is a real recovery starting, but I don't think you can be sure, yet."

General Motors Corp. officials acknowledged that this year's figures seem high because of last year's disappointing performance. But "favorable economic developments" nationally should help the company "continue strong sales in the spring and summer," said Robert D. Lund, GM vice president of sales and marketing.

Lund said the interest rate programs, coupled with signs of economic improvement, "has added significantly to both showroom traffic and sales momentum."

GM, Ford Motor Co. and Chrysler Corp.--the nation's three largest automakers--tagged an 11.9 percent annual interest rate on their new car sales in the first quarter of this year. GM and Ford on April 1 replaced the 11.9 percent program with 9.9 percent financing on selected small cars and compact trucks.

The sales strategy helped GM sell 104,978 new cars April 1-10, a 27.5 percent increase over 76,093 GM cars sold in the same period last year. But Ford's sales dropped to 32,214 cars from 36,913 cars sold last April 1-10.

Chrysler Corp. sales also fell in early April to 19,845 cars from 20,852 in the year-ago period. But Chrysler's daily selling rate was up 7.1 percent for the period at 2,841 units per day, because the 1982 early April period included one more selling day.

American Motors Corp. reported 52,295 cars sold, or 623 per day in 1983. That is up 118.6 percent from the 24,252, or 285 per day, sold by this time last year.

Volkswagen of America continued to lose ground in its bid to sell its domestically produced cars. VW reported 889 new-car sales for early April, down 62.1 percent from the 2,343 units sold last year.