Domestic automakers broke a four-month string of sales increases today, reporting a 3.4 percent drop in February, although sales for the final 10 days increased 1 percent.

Analysts blamed poor weather on both coasts for the monthly domestic decline, plus consumer disinterest in the 11.9 percent financing rates offered on new cars and trucks.

Sales of imported cars, meanwhile, rose 6.4 percent during the month.

The five American firms said they sold 441,226 cars in February, down from 456,942 in February 1982. The annual selling rate in February was 6 million cars compared with 6.3 million in the month last year.

In the Feb. 21 to 28 period, automakers had one extra day in which to sell cars, which accounts for the apparent disparity in some figures. They sold 173,852 cars, up 1 percent on a daily rate basis from 147,517. The daily rate for the period of 24,836 was up slightly from last year's 24,586.

American Motors Corp. posted the biggest increases of the domestic companies. Due to the success of the Renault Alliance, AMC sales were up 105 1/2 percent in February. AMC sold 5,595 cars in the final 10 days, up 104.3 percent on a daily basis from 2,344 last year.

Chrysler Corp., which offered a choice of rebates or lower financing rates, was the only Big Three automaker to post a sales gain for the month. Its sales were up 3 percent from last year. It marked the sixth consecutive month in which Chrysler sales have risen.

Chrysler sales in the final 10 days were 25,351, down 4 percent on a daily rate basis from 22,575.

General Motors Corp. had a 5.4 percent drop in February sales. But its sales of 101,319 for the final 10 days were up 2.8 percent on a daily basis from 84,509 last year. So far this year, GM sales are up 3.4 percent.

Ford Motor Co. had a 7.8 percent sales decline in February. Its sales of 39,000 autos for the final 10 days were down 4.2 percent on a daily basis from 34,902 last year.