Long-time employees at the Defense Intelligence Agency have until April 30 to take advantage of a special "early out" retirement bonus.

Many Defense employees are hoping for a similar early-out break, but for now, only three Army installations for now, only three Army installations besides the DIA - in New Jersey, Colorado and Kentucky - have authority to permit early retirement because of major of cutbacks and consolidations.

Other Defense activities, and other federal agencies hit by job cutbacks or reorganizations, are prepared to ask permission to allow long-time employees to retire early to save the jobs of younger, and less senior aides who, otherwise, would be the first fired in any reduction in force. So far, however, only the DIA here, and Army civilians in Lexington, Ky., Dover, N.J., and Pueblo, Colo., have the early-out option.

Several things must happen before an agency can request, much less get, authority to let senior workers retire early. They include:

(1) An agency or installation must be in the midst of, or facing a major reduction in force.

(2) It has to sell its parent agency on the idea of early retirement and the parent agency must convince the Civil Service Commission and get CSC's okay.

(3) The early'out authority can be agency-wide and nationwide or it can be limited to a special geographic region, part of an agency or even to certain grade and career fields.

(4) Employees who want to take advantage of it must have either 25 years' service. They must, in effect, "volunteer" to be "involuntarily retired," thereby qualifying them for immediate pensions. Those annuities are reduced by 2 per cent for each year the individual is under age 55.

DIA, which is trying to eliminate 250 of its 2,000-plus civillian jobs here, can offer the early-out option to emplyees who meet the age and or service requirements through April 30. Without it, DIA estimates it would have to fire as many as 120 people.

The idea of early retirement is attractive to many employees, but it isn't easy to come by. When Congress wrote the law in 1973, it specified that the early-out was to be used selectively by agencies to avoid adverse impact on employees because of a reduction in force.

Defense, which employs about half the federal work force, has used the early-out retirement plan 45 times since it became law. Except in two cases, the retirement option was limited to specific areas or bases.