American Motors Corp. earned $12.8 million in the last three months of 1979, AMC said yesterday in Detroit. That was 32 percent below the corresponding figure for 1978, but still the second best performance for the quarter in the company's history.

Sales for the quarter, the first of AMC's fiscal year, were a record, but the increase came in less profitable vehicles.

The report may turn out to be the brightest by any automaker of the quarter. Chrysler Corp., Ford Motor Co. and General Motors Corp. report results for the quarter next month, and analysts expect only GM to show a profit.

The $12.8 million profit (37 cents a share) compared to profits of $26.2 million (86 cents), including $7.2 million in special tax credits in the same period last year. Exclusion of those credits would leave $18.9 million in operating earnings (62 cents) comparable to the $12.8 million.

Sales of $789 million were 10 percent higher than the $715 million recorded in the first quarter of the previous fiscal year.

Wholesale sales of AMC and Renault cars worldwide rose 42 percent to 65,772, while Jeeps fell 30 percent to 37,600, AMC said. That was Jeep's second-best second quarter.

Pullman Inc. has reported record income from continuing operations in 1979, although it experienced an overall decrease in income because some operations were dropped.

The Chicago-based international corporation announced Wednesday that its income from operations it continued in 1979 was $93.7 million ($8.50), up 27 percent from $73.6 million ($6.71) in 1978.

But the company said its overall net income was down in 1979, largely because the corporation discontinued manufacturing rail passenger cars.

In its statement, Pullman said its net income in 1979 was $47.9 million ($4.34), down from 1978 net income of $63.9 million ($5.83).

C. P. Lattin Jr., Pullman's president and chief executive officer, said, Revenues and profits from continuing transportation equipment manufacturing operations set new records in 1979."

At the end of the first quarter in 1979, Pullman announced it would discontinue its rail passenger car manufacturing operations after it completes outstanding contracts. The statement said Pullman's only significant outstanding passenger car contract is with Amtrack.