A worker earning $15,000 a year who retired in 1984 after 30 years in a company pension plan would have collected $385 a month in retirement benefits under the typical plan in effect in the nation's medium and large business firms, according to a Bureau of Labor Statistics report.

Further up the income scale, a $40,000-a-year worker with 40 years in the plan would get $1,075 a month in retirement benefits, BLS economist Donald G. Schmitt calculated in the study published in the government's Monthly Labor Review.

Combined with Social Security benefits, the pensions provided by many of the plans would give workers retirement incomes ranging from 50 percent to 100 percent of their prior annual earnings, Schmitt said.

The findings were based on benefit formulas used in 832 different pension plans in medium and large firms. In general, pension benefits are more common and better in such firms than in smaller ones.

In order to determine what the typical pension plan would pay under various conditions, the BLS calculated benefits that would have been paid if the worker had retired at 65 in 1984, had been earning the specified amount in the last year of work and had one of several different typical work and salary histories prior to the final year.

Both the pension levels and the preretirement earnings levels used in the study are figured before payment of any taxes.

Looking at the combined averages for all types of workers in the firms, the study found that, excluding any Social Security benefits:

*The monthly pension for a worker with 10 years in a pension plan prior to retirement would be $137 a month if the salary the year before retirement was $15,000; a pension of $242 if the salary was $30,000; and a pension of $326 at $40,000.

*For a worker with 20 years of coverage prior to retirement, the pension would be $263 if the salary was $15,000; $462 if the salary was $30,000; and $623 if it was $40,000.

*For a worker with 30 years of pension coverage prior to retirement, the pension would be $385 if the salary was $15,000; $662 if it was $30,000; and $886 if it was $40,000.

*And for a worker with 40 years of pension coverage, the monthly pension would be $486 if salary was $15,000; $814 if it was $30,000, and $1,075 if it was $40,000.

The study found that, generally, white-collar pensions tended to be higher than blue-collar ones for workers at the same salary and coverage levels, "except at the lowest earnings level ($15,000), where production workers had slightly larger benefits."

The BLS study also calculated how much the retiree would receive in combined private pension and Social Security benefits. The result was expressed as a percentage of final year salary. This is the so-called "replacement ratio" showing how much of the final year's salary would be replaced by combined pension and Social Security benefits after the worker stopped his job. Many experts believe the replacement ratio must be at least 60 percent to 80 percent to maintain previous living standards.

The calculation assumed the person worked 40 years in jobs subject to Social Security tax, but only the specified years in jobs with private pension coverage. The study found:

*For workers with 10 years in the employer pension system, the replacement ratio from combined pension and Social Security benefits, excluding benefits for a spouse, was 54 percent if the final salary was $15,000; 37.5 percent if the final salary was $30,000, and 30.9 percent if the final salary was $40,000. When the Social Security spouse benefit is included, the replacement ratios would be 75.4 percent ($15,000); 51.4 percent ($30,000); and 41.4 percent ($40,000).

*For workers with 20 years in the employer pension system, the replacement ratio from combined pension and Social Security benefits would be 64 percent for a $15,000 worker excluding the spouse benefit, and 85.4 percent including it. It would be 46.3 percent for a $30,000 worker excluding the spouse benefit, and 60.2 percent including it, and 39.8 percent for a $40,000 worker (50.3 percent including spouse benfit).

*For workers with 30 years in the employer pension, the ratio would be 73.8 percent if salary was $15,000 (95 percent with spouse benefit); 54.3 pecent if the salary was $30,000 (68.2 percent including spouse benefit); and 47.7 percent if salary was $40,000 (58.2 percent with spouse benefit).

*For workers with 40 years in the employer pension system, the replacement ratio would be 82 percent if salary was $15,000 (103.2 percent with spouse benefit); 60.4 percent if salary was $30,000 (74.2 percent with spouse benefit) and 53.3 percent if salary was $40,000 (64 percent with spouse's benefit).