The number of older persons in Fairfax County who have rejoined the area's work force almost doubled in the last half of 1985, according to Senior Employment Resources, a nonprofit job placement agency for persons 55 years of age and older.

Senior Employment Resources Executive Director Bob Revere said that between July 1 and Dec. 31, 1985, his agency found jobs for 280 retired or older persons in Northern Virginia, compared with last fiscal year's total placement of 198 persons.

"We've been bombarded with calls," Revere said. "A lot of older people are experiencing a post-holiday blues, and there's nothing quite like a job to get busy."

Founded in 1983 by Arthur Boyd, a business consultant, Senior Employment Resources was originally funded solely by the federal government and primarily helped low-income persons over 55 and refugees over 45 reenter Fairfax County's job market. In October 1985, the county's Board of Supervisors awarded a $30,000 grant to the job bank, enabling the organization to expand its services and reach out to the portion of the county's older population that was not poverty-stricken.

Senior Employment Resources still helps some needy senior citizens and refugees with retraining and finding jobs, but now it is the only free job placement agency in Fairfax County that focuses almost exclusively on older workers who do not need public assistance.

Revere said most of his clients are placed in full-time secretarial, receptionist or bookkeeping jobs, but there are still hundreds of part-time minimum wage positions that remain unfilled and unwanted by the county's senior population.

These lower paying jobs include cashier, over-the-counter service at fast food restaurants, retail sales and telephone solicitation. Part of the difficulty in filling the more menial jobs, Revere said, is in the $3.35 hourly minimum wage.

"An employer has to realize that people with 30 or 40 years' experience in the work force don't want to go back to work at minimum wage," said Revere. "The salaries are just unrealistic."

Revere said employers at most fast food restaurants would rather attract younger people or students to work behind their service counters. "But there are a lot of people over 55 years old who come into fast food restaurants after the rush is over and like to sit and have a cup of coffee."

Revere said he has a fast turnover in jobs that pay between $5 and $7 per hour, such as clerical positions, market research and general office duties.

"Employers are beginning to realize that people who are older don't have to be trained as much . . . . They don't move around; they have a job and they stick with it," said Revere. "Some employers are finding it difficult to find skilled people for jobs, so they come to the older population where they can get a good employe for the money."

Jarold A. Kieffer, chairman of the board of Senior Employment Resources, said two-thirds of the Annandale-based agency's clients are women who are widowed, separated or "their life is jarred some other way," with incomes between $7,000 and $10,000 a year.

Kieffer said that when county officials awarded the grant to Senior Employment Resources in October, they recognized that the agency was not adequately meeting the social needs of the area's senior citizen population by serving only the poverty-stricken elderly and refugees.

" The supervisors recognized a simple fact of economic life: A lot of people in this county are not living in poverty, but if they didn't have some way of supplementing their income they would be," said Kieffer, who also was staff director of the 1981 White House Conference on Aging and was deputy commissioner of the Social Security Administration under President Ford. "It's almost self-defense in a way, because down the road those elderly won't be on the public assistance rolls. I call it intelligence in how you head off something."

Kieffer said he would like to see Senior Employment Resources offer jobs that pay between $20,000 and $40,000 a year.

Revere said Senior Employment Resources operates under the philosophy that it is not too late for persons 55 years of age and older to start second careers. "As long as they are helping, they have a contribution to make to society. They can be converted from tax users to taxpayers."