Human Services Group Inc.--a privately owned consulting, investment and real estate firm based in Bethesda--reported yesterday that it controls about 5.2 percent of the stock of American Security Bank, the District's second-largest commercial bank.

Human Services said in a formal required filing with the Securities and Exchange Commission that it has acquired 187,600 shares of American Security. Melvyn J. Estrin, chairman of Human Services, said the company has been acquiring the bank's stock for the past year or so, but would make no further comments on the acquisition. "The response is in the 13-D"--the SEC filing--Estrin said.

In that filing, Human Services said that it bought American Security's stock as an "investment" and "has no present plans" to change its position by purchasing enough stock to gain control. But the firm put in a caveat that it intends to continue to review its holdings and could change its mind.

Last year, former Washington Star owner Joe L. Allbtritton bought the biggest block of stock in Riggs National Corp., which owns Washington's biggest bank, and became the parent company's chairman.

A spokesman for American Security said the bank has been aware of Human Services' purchases for some time, but would make no further comment. Human Services becomes the fourth-biggest shareholder in American Security. The bank owns 13 1/2 percent of its own shares. A combination of four electrical worker pension and benefit funds owns 7.7 percent, while A. James Clark owns 6.1 percent. Clark is president of Clark Enterprises Inc., a company that owns the Omni and George Hyman construction companies.

As of April 6, there were 3.626 million shares of American Security outstanding.

According to the formal filing, the SEC instituted administrative proceedings again Human Services for failing to file disclosure forms with the agency between 1972 and 1979 in connection with its purchase of American Health Services Inc. In 1980, Human Services "consented" to the SEC's charges without admitting it had done anything wrong. The company was ordered to comply with reporting requirements and file delinquent forms. The forms in question were the very 13-D that the company filed yesterday in connection with its purchases of American Security stock.

Estrin would not give any financial details about Human Services, whose stock is owned completely by Estrin and four other officers and directors of the company: President Hyman Frankel, Vice President Charles Aboud, Secretary Sheldon Steinberg and Vice President Gary Jonas. Estrin was once a partner in the Gangplank restaurant and Tomfoolery restaurant.

He said Human Services has been in business for 12 years and is involved in a number of businesses ranging from research and development to real estate to investment to management consulting.

American Security, which traded as high as $45 to $46 a share a year ago, has been trading in the $37 range recently, although volume in the stock has been slow. Sources said an investor tried to sell about 100,000 shares of the stock several months ago, contacting possible purchasers privately. The big block apparently never was sold, according to local securities analysts and traders.

But many investors know the big block of American Security exists, and that has helped depress the price from its highs of last year, according to one analyst. Human Resources detailed its purchases of 21,600 shares of American Security stock during the past 60 days and said it paid prices that ranged from $36.50 to $39.50 a share. American Security stock is traded over the counter.

Eliot Benson, vice president and research director of Ferris & Co., said that American Security is a good investment, both from the "standpoint of the sizable presence" it has as the District's biggest bank and its growth potential if federal laws are relaxed to permit interstate banking.

Estrin said he feels American Security is a "good, solid bank" whose stock price has been attractive relative to its intrinsic value.