NEW YORK (AP) _ Lee A. Iacocca's $20.5 million in salary, stock options and bonuses made him the nation's highest paid executive last year, according to Business Week magazine's annual survey of executive compensation.

In its May 4 edition released Thursday, the magazine said Paul Fireman, chairman of shoemaker Reebok International Ltd., placed a distant second with $13.1 million in total compensation.

Victor Posner, the financier who held the top spot in 1985, placed third last year with $8.4 million in salary and bonuses from one of his holding companies, DWG Corp.

Coincidentally, DWG reported Thursday that it lost $8.4 million in 1986 on revenue of $1.1 billion.

Much of Iacocca's 1986 compensation came from a lump-sum payment of Chrysler stock and from the exercise of stock options he had accumulated over his seven-year tenure as head of the nation's third largest automaker.

After being elected Chrysler's chairman in September 1979 when the company was near bankruptcy, Iacocca worked one year for a token $1. But he also began receiving a variety of stock options and other incentives that proved valuable once Chrysler recovered.

Business Week, which compiled its survey with Standard & Poor's Compustat Services Inc., said that among the 317 companies studied, the average salary and bonus for the chief executives jumped 17.9 percent last year to $829,887.

That was nearly double the 9 percent average increase in 1985, even after excluding the total of $22 million in one-year bonus payments to Iacocca and Fireman, it said.

Together with a 56 percent rise in long-term incentive compensation, such as stock options, the chief executives' total average pay climbed 29 percent last year to $1.2 million, the magazine said.

Most managers and ''run-of-the-mill executives'' at the 317 companies received raises of less than 6 percent last year, it added.

Here are the seven other highest paid executives in 1986, followed by their total compensation:

-John J. Nevin, chairman of Firestone Tire & Rubber Co., $6.36 million.

-Charles E. Exley Jr., chairman of NCR Corp., $6.30 million.

-Sidney J. Sheinberg, president of MCA Inc., $6.08 million.

-Maurice R. Greenberg, president of American International Group Inc., $4.60 million.

-Donald E. Petersen, chairman of Ford Motor Co., $4.34 million.

-Rand V. Araskog, chairman of ITT Corp., $4.26 million.

-Alan C. Greenberg, chairman of Bear Stearns Cos., $4.08 million.