About 95 percent of the employes of medium and large U.S. firms were covered by health insurance provided through the job last year, 89 percent by a retirement plan and 96 percent by life insurance, according to a Labor Department survey released yesterday.

The survey provides representative data for more than 21 million workers employed by firms with at least 100 to 250 workers, depending on the industry.

The survey also found that about 94 percent of the workers had some protection against income loss due to temporary illness -- either a sick-leave benefit or some form of sickness and accident insurance. About half also had protection against long-term disability.

The results are representative only of workers at medium and large firms, not the whole U.S. labor force. Benefits in smaller firms often are less favorable.

The study, published by the Bureau of Labor Statistics, showed that virtually all the employes were given paid holidays, vacations and time off for jury duty; 88 percent got funeral leave and 72 percent got rest time.

On the average, the BLS said, covered employes could expect the following benefits: rest periods of 26 minutes a day (most prevalent among production workers); 10 paid holidays a year; nine days of vacation after a year on the job, 16 days after 10 years and 21 days at 20 years; three days of funeral leave per death; 12 days of military leave, and 15 days of sick leave at full pay at one year of service, plus jury time off as needed.

In health plans, about 60 percent of the workers paid nothing for coverage for themselves -- the employer paid the whole cost -- and one-third paid nothing for dependents.

Virtually all had plans providing hospital, surgical, diagnostic and some form of mental health care, and 80 percent had protection against catastrophic expenses, either through a "stop-loss" provision or enrollment in a health maintenance organization. Nearly three-quarters had dental benefits, and a third would receive some employer-financed health benefit during a layoff.

In the retirement area, 89 percent were covered either by a defined benefit plan or a defined contribution retirement plan, or both. The study found that 76 percent of the employes were covered by defined benefit plans, in which there is a set formula for determining annual benefits on retirement.

About 47 percent of the workers had a defined contribution retirement plan -- for example, a profit-sharing or deferred wage arrangement such as a 401(k) plan. In the latter, wages are set aside from the worker's salary for distribution on retirement and are not taxable until then; the employer usually makes a matching contribution, most frequently at the rate of 50 percent of the first 6 percent contributed by the employe.

The study included figures on average benefit rates that would be received by a worker in 1986 from combined Social Security and defined-contribution pensions for those who had them.

Such a worker, retiring at 65 and having 40 years of employment, the last 25 in the job providing the pension, would receive the following benefits: If his (or her) final year salary was $15,000, the combined Social Security and job pensions would come to about $10,400. If the final year's salary was $30,000, the figure would be about $15,840, and if it was $40,000, the combined benefit would be $18,560.