Goodbye, obscurity. Hello, popularity. Only a few months ago, Mid Atlantic Medical Services of Rockville was deep in the pink sheets, that list of stocks that are not traded on any organized exchange. Today, Mid Atlantic is trading on Nasdaq's electronic National Market System, it has 10 brokerage firms buying and selling its shares and the company has been "discovered" by the public.

What investors, including mutual funds and other major institutions, have discovered is that Mid Atlantic operates a sizable Washington area health maintainance organization (HMO), which is growing rapidly and showing sharp profit increases.

That insight has been enough to bring waves of buyers into the market recently and Mid Atlantic stock, which was selling at $5.50 on Jan. 1, closed Friday at $15, up 173 percent.

Indeed, health-oriented stocks, including those of HMOs, have been sought-after investments in recent months. One of the biggest gains shown by a mutual fund in the second quarter of this year was by the Fidelity Select Medical Delivery Fund, which soared 21 percent.

That result may surprise some investors who remember a time, not very long ago, when the shares of HMO companies were faring badly.

Analysts Mack Faulkner and E. Hunter Thompson Jr. of Branch, Cabell & Co., in Richmond, noted in a recent report that almost 75 percent of the HMO industry was unprofitable in 1987 and 1988, thus depressing the price of HMO stocks.

But profits in the HMO industry turned around in 1989, they said, and HMO stocks rebounded.

"We believe stocks of well-managed HMOs should continue to show substantial price appreciation, given the recent consolidation in the HMO industry and continued pricing flexibility," the analysts wrote.

George T. Jochum, president of Mid Atlantic, said the HMO industry got into trouble in 1987 and 1988 because the business was growing so rapidly that the costs of expansion outpaced revenue. As competitors fell by the wayside, and as the pool of HMO members grew, the surviving companies found that their profits were moving up, Jochum said.

Analyst Peter J. Grua of Alex. Brown & Sons in Baltimore, said that the HMO industry has been "in a period of recovery" as the result of continued consolidation, improved pricing and better-managed balance sheets.

Companies such as Mid Atlantic tend to benefit during periods of economic weakness, Grua added. "They do better when the economic environment is poor because employers try to control their benefit costs," he said. In so doing, they turn to HMOs.

Grau said he recently visited Mid Atlantic and found that "They seem to have a lot of things going the right way." He noted, however, that the Washington metropolitan area is one of most competitive health-care areas in the nation.

Mid Atlantic says it has a 13 percent share of the health care business in the Washington area.

One of the powerful influences on Mid Atlantic's performance, Faulkner said, is the fact that increases in health premiums are expected to keep pace with the rise in medical costs during the 1989-1990 period.

Revenue per member will move up an estimated 11 percent, he said, while medical costs per member are expected to rise by 9 percent.

Mid Atlantic offers a variety of health services.

The major offerings are MD-IPA Health Plan, M.D. IPA Preferred and Optimum Choice Inc. Together they have 214,000 members. Two other service units cover an additional 68,000 individuals.

Mid Atlantic's financial performance has been strong. Operating revenue in 1989 was $116.5 million, up 29 percent. Profits were $3.1 million, up 50 percent.

The first-quarter performance also was impressive. Revenue grew to $43.5 million, up 67 percent. Net income rose to $1.85 million, up 129 percent.

And with the second-quarter reports only days away, Mid Atlantic officials have said they are comfortable with analysts' estimates that the company will earn 15 cents to 20 cents in the quarter and $1 to $1.25 a share for the year. The firm earned 46 cents a share in 1989.

The second-quarter activity prompted Faulkner to boost his 1990 earnings estimate to $1 from 90 cents and to say that he believes the stock is reasonably priced. Faulkner also raised his 1991 estimate to $1.35 from $1.25.

Mid Atlantic is expanding its services geographically.

It now has health providers in every Maryland county, Jochum said. That fact is a major advantage when his firm is trying to sell its health services to a large company with employees in many parts of the state.

Mid Atlantic is moving into Richmond, Norfolk and the Tidewater area and hopes to be able to blanket the state of Virginia within three years, he said.

In the future, Jochum said, the company may head for Delaware and Pennsylvania.

The boost in Mid Atlantic stock has been accompanied by a sizable increase in trading activity. Among the regional firms that make a market in the stock are Ferris, Baker Watts; Scott & Stringfellow and Koonce Securities.

One of the brokers who has watched the evolution of the company from its earliest beginnings is L. Victor Seested Jr., special managing director at Ferris, Baker Watts in Rockville. He has been trading the stock since 1988, when it was owned chiefly by company officers and directors and participating physicians.

Now, he says, the trading has broadened considerably.

Today, officers and directors, many of whom are physicians, own about 24 percent of the 6.9 million shares outstanding. But it is not clear how much stock is still owned by doctors. Clearly, many of the shares originally held by the physicians have moved into the market place as the price has gone up.

Indeed as of March 5, there were only 537 shareholders of record. No one is quite sure how many shareholders there are at the moment. But the company would not be surprised to find out that, like the rest of its business, the number of shareholders has multiplied faster than they ever imagined.

Is the market for environmental stocks hot? It certainly would seem so if you judge by the stock offering completed Friday by Environmental Elements Corp., of Baltimore. Simply put, the deal went better than expected.

The company had planned to offer 2.3 million shares but sold 2.475 million shares. The estimated price was $14 to $16 dollars a share but the company got $16.50 a share. That doesn't happen very often these days.

The sale brought in a total of $40.8 million, of which about $29 million went to the company, before expenses, while the rest went to insiders who were selling stock.

Environmental Elements, as we noted in June, is a company in the anti-pollution business, which had an unprofitable past and has an uncertain future, largely because the big federal and state bucks for cleaning up the air may be a long way down the road. But environmental stocks, as a group, have been selling at handsome prices in recent months.

The underwriters were Kidder, Peabody & Co. of New York, and Legg Mason Wood Walker Inc. of Baltimore. And the deal, you may recall, had a special wrinkle.

That is, Legg Mason owned 13.6 percent of the stock of Environmental Elements while Raymond A. "Chip" Mason, chairman of the brokerage firm, owned 6.6 percent of the stock. For five years, Mason was chairman of Environmental Elements.

Shares of stock were sold not only by the company but also by Mason who got about $922,000 for his stock and by Legg Mason, which got about $2.3 million. Chairman Richard E. Hug, who recently gave up the title of chief executive officer, sold stock worth about $4.6 million.

Even so, insiders will continue to control more than half of the company's stock.