American Motors Corp. yesterday reported that it suffered a $6.7 million loss in the final quarter of 1985, bringing its loss for the year to $125.3 million.

Also yesterday, Zenith Electronics Corp. posted a $7.7 million loss for 1985.

AMC said most of the red ink was incurred in the first half of the year and that losses have been cut substantially in recent months. Nevertheless, the 1985 showing was far short of the $15.5 million profit the auto maker reported in 1984.

Income for the year also was down, to $4 billion compared with $4.2 billion in 1984, the company said. In the quarter, sales were $1.13 billion compared with $1.06 billion in the 1984 period.

The company lost $622.5 million from 1980 through 1984.

AMC President Jose Dedeurwaerder issued a statement reiterating the company's position that it won't show significant profits until a new auto assembly plant in Brampton, Ontario, begins making cars next year.

For the past several years, AMC's U.S. car operations in Kenosha, Wis., have had dismal sales, while the company has been able to make high profits on Jeep utility-vehicles made in Toledo. Jeeps sold at record rates during 1985, and the company projects a better year for 1986.

AMC was the last of the four U.S.-based auto makers to report 1985 earnings. The Big Three reported combined profits of $8.1 billion, with General Motors Corp. at $4 billion, Ford Motor Co. at $2.5 billion and Chrysler Corp. at $1.6 billion.

Most of the new AMC products to debut in the next year will come, not from domestic operations, but from the overseas factories of Nationale des Usines Renault, the French government-owned auto maker that controls AMC with a 46 percent stock ownership.

The $125.3 million loss for the year was the equivalent of a negative $1.24 a share, compared with a gain of 4 cents a share a year earlier.

*Zenith Electronics Corp. reported a loss of $7.7 million, or 33 cents per share, in 1985.

The company blamed large price declines for consumer electronics products and significantly lower sales of power supplies and cable products for the loss.

Zenith's earnings for 1984 totaled $63.6 million ($2.88), including a one-time tax adjustment gain of $10.4 million (47 cents).

Sales for 1985 totaled $1.6 billion, down 5.3 percent from $1.7 billion in 1984.

Fourth-quarter net income was $3.6 million (16 cents), down 68.1 percent from $11.3 million (51 cents) for the fourth quarter of 1984. Fourth-quarter sales totaled $484 million each year.