DETROIT (AP) _ Domestic automakers reported an increase in auto sales in mid-May - their first of the year - but dealers weren't much encouraged by the figures released Thursday.

U.S. sales of North American-made cars and light trucks rose 6.7 percent in mid-May, but the gain came against the mid-May period of 1990, one of the weakest sales periods for all of last year.

''It seemed that last year at this time it was about the worst that it had gotten,'' said Paul Giovino, sales manager at Jerry Roth Automotive Centers in Lakewood, Colo., which sells Chevrolet, Geo, Isuzu, Daihatsu and Peugeot cars outside Denver.

''Then in June, we almost doubled our business right through to September or October,'' he said. ''In November it fell off and hasn't come back since.'' The increase Thursday was the first for a 10-day reporting period since a 22.5 percent increase in early December.

Nine of the 10 major U.S. automakers reported combined car and truck sales for the May 11-20 period averaged 29,433 a day, compared with an average of 27,092 during the same period last year.

General Motors Corp.'s car and truck sales during the period rose 12.2 percent and Ford Motor Co.'s mid-May sales rose a skinny 1 percent. Sales of cars with Japanese nameplates were mixed.

Chrysler Corp. doesn't release 10-day sales figures. An Associated Press estimate, based on the company's average monthly market share over the previous 12 months, showed the No. 3 automaker's mid-May sales fell 3.2 percent compared with last year.

The auto industry has been mired in a slump since late 1989, and has been crippled by the recession and the Gulf War since then.

Some industries have shown brief signs of recovery. The government on Thursday reported an increase in factory orders for durable goods. It also reported growth in auto orders from dealers to manufacturers last month.

But the mid-May sales figures, although higher than last year's, didn't indicate a strengthening of new-car sales. In mid-May last year, the sales rate plummeted to one of its low points for all of 1990, as the Big Three pared their incentive programs.

A more accurate picture of the auto industry's woes shows up in year-to- date figures. Through May 20 of this year, including the Chrysler estimate, sales of North American-made vehicles were down 15.4 percent, falling to an average daily rate of 30,050 compared with an average rate of 34,530 during the same period last year.

Tom Webb, senior economist with the National Automobile Dealers Association in McLean, Va., said the sales rate in mid-May appeared to be better than the miserable rate last month.

''April sales were so disappointing that I think we are just returning to a more normal level,'' Webb said.

GM's combined mid-May domestic car and truck sales rose 12.2 percent, with car sales up 13.4 percent and truck sales up 10 percent. GM's sales of domestic vehicles since Jan. 1, however, were down 16.6 percent.

Ford said its mid-May domestic car sales rose 1.3 percent and truck sales increased 0.5 percent for a combined 1 percent increase in vehicle sales. But for the entire year, Ford's sales were down 19.5 percent.

Among the Japanese companies making vehicles in North America, Honda sales rose 28 percent for mid-May but were down 5.7 percent so far this year.

Toyota's sales of North American-made cars tumbled 29.6 percent in mid-May compared with last year and were 22.9 percent lower for the entire year.

Nissan's combined car and truck sales were up 49.3 percent in mid-May and up just 4.2 percent for the entire year.

Mazda said sales of its North American-made cars and trucks fell 13 percent in mid-May and rose 51.1 percent for the entire year.