The average engineer in the Washington metropolitan area earns close to $39,000 a year, with the federal government paying about one-third more than private industry, according to a survey by the Institute of Electrical and Electronics Engineers.

The survey also showed that salaries of government engineers jumped 20 percent over the past 18 months while salaries of engineers working in private industry increased at 12 percent. ccording to the survey, the average government engineer earns almost $45,000 while the average engineer in private industry makes $33,798. A senior, nonsupervisory engineer working in a private industry earns an average of $37,000, the survey showed. The top salary recorded was $100,000 paid to an engineer in private business.

The reason for the higher average salaries of federal engineers, the institute said, is that the government employs a far higher proportion of its engineers in senior, supervisory ranks than private industry. The survey found 87 percent of the government engineers are in the top three grades compared to 26 percent of the industry engineers. By contrast, government engineers at the working level--the bottom five grades--earn about 9 percent less than their private industry counterparts.

The survey covered 3,515 engineers, about 10 percent of the total number believed employed in the Washington area. The engineers in the survey work for 17 private businesses and two federal agencies that answered questionnaires sent out by the institute. The engineers covered were almost evenly divided between government and private industry. While the IEEE did not claim the sampling was scientific, it said the results agree with those in similar surveys taken by other organizations.

A companion survey, sent to institute members only, showed similar results, though the average salary turned out slightly higher--$42,250--because IEEE members tend to be on the higher rungs of the profession.

While the average salary for all engineers was $38,864, electrical engineers earned slightly more--$39,680--reflecting a greater demand for their skills. A listing of the hardest engineering jobs to fill is headed by electrical engineers specializing in computers, while mechanical and design engineers are low on the list.

Large companies pay more than small ones--$34,384 compared with $30,565--and firms specializing in research and development pay higher salaries ($35,797) than manufacturing companies ($33,653) or support contractors ($31,406).

The salaries of women engineers ran about $10,000 to $11,000 below that of men, but the survey showed they had substantially less experience and their age averaged about 10 years younger than men. The same was true for blacks, though Hispanics in the engineering profession were slightly older and more experienced and had higher average salaries, the survey showed.