Twenty-six area companies -- ranging from defense contractors and computer firms to a temporary-help company and a rental car franchisor -- made this year's list of the 500 fastest-growing private companies published this week by Inc. magazine.

"I'm elated," said William F. Simmons, president and cofounder of Group Benefit Services of Hunt Valley, Md., which at number 22 on the list was the highest-ranked local company.

Inc. ranked the companies by percentage growth in sales between 1982 and 1986.

Simmons' firm is part of a new and fast-growing industry called third-party administration, which is involved with the management of health care benefits for employers.

Group Benefit Services manages benefits programs for 20 trade associations, including much of the construction industry in Maryland.

According to Inc., Group Benefit reported more than $11 million in sales in 1986.

Simmons said the firm is on target for about $50 million this year.

Such frenetic growth is typical of firms on the Inc. list.

RJO Enterprises, a Lanham company that provides systems engineering services and was number 24 on the list, reported $14.8 million in sales, a 5,510 percent increase over $263,000 sales in 1982.

Integrated Systems Analysts, an Arlington defense contractor, reported a 3,907 percent increase, to $21.1 million in sales in 1986 from $526,000 in 1982.

Heading the Inc. 500 was American Photo Group of Atlanta, a photo-finishing production and marketing firm.

It experienced a 52,244 percent growth in sales between 1982 and 1986.

The company had sales of $78.0 million in 1986, up from $149,000 in 1982.