Mid-March Sales Off 3.3% for N. American-Made Cars : Autos: But analysts say the drop is due to a slump in fleet sales and that the retail side remains strong.

Big auto makers said Tuesday that sales of North American-made vehicles fell 3.3% in mid-March, but analysts, noting that the drop was due to a slump in commercial sales, appeared unconcerned.

Fewer sales to car-rental companies explained part of the overall drop, auto makers and some analysts said. Retail sales, which generate more profit for auto makers, apparently compensated for some of the decline in fleet sales.

“The retail side is still up pretty nicely,” said Steve Girsky, an auto analyst with Paine Webber Inc. in New York. “That being the case, I feel no need to panic.”

The nine makers who report results said they sold cars and trucks at a daily rate of 26,188 in the March 11-20 period, compared to 27,012 in the same period a year ago.

For the year to date, overall vehicle sales are up 4.4% over recession-wracked 1991. Big Three sales for the year are up 3.5%, and sales of domestically made vehicles with foreign nameplates--known as transplants--are up 11.1%.

Both General Motors Corp. and Ford Motor Co. reported lower car sales in mid-March. Ford, however, saw a 13.6% increase in truck sales, pushing its total vehicle sales up 2.3%.

GM said its car sales fell 6.1% and light truck sales were off 12.6% in the period. The No. 1 auto maker’s total mid-March vehicle sales were off 8.4%.

Chrysler Corp., which reports sales only monthly, had an estimated 4.5% drop in vehicle sales. The Associated Press bases its estimate on Chrysler’s average market share for the previous 12 months.

Recent agreements with car-rental companies, many of which are owned by auto makers, have cut into the auto makers’ sales by extending the period of time the cars are in the field to six months from four months. After that period, auto makers buy the vehicles back and resell them to consumers at deep discounts as “program cars.”

GM spokesman Terrence P. Sullivan said that through early March, the portion of GM’s cars going to fleets was about 3.5 percentage points lower than a year ago.

Truck sales continue to be one of the few consistent bright spots of the year, with the Big Three and Japanese makers Isuzu and Toyota all showing strong sales of light trucks.

Light trucks and vans also are an alternate choice for family transportation and may be up to 40% of the vehicle mix, Girsky said.

Among Japanese car companies making vehicles in North America, Toyota’s 38.8% auto sales increase was the biggest gain in the period. Toyota just recently began selling North American-built trucks, making any comparison with 1991 impossible.