The folks at Microlog Corp. in Germantown make voice-message systems for a living. But, at times, it seems that they should really be in the roller coaster business. Few companies have seen their stock rise and fall so often and so fast.

Microlog is a 22-year-old firm that sold stock to the public for the first time in 1986. In 1987, the company, then known as Old Dominion Systems Inc., suffered a loss that sent the stock down 69 percent. A profit rebound in 1988 brought the stock back up 120 percent.

In 1989, when Microlog won a series of voice-message contracts from major firms, Microlog's profits soared and its stock rose 246 percent, making it the year's top gainer in the Washington area.

But then in 1990, as the big contracts were replaced by smaller ones, the company chalked up a $475,000 loss and the stock fell 81 percent. Microlog shares, which had once been as high as $13.75, closed last year at $1.81 each.

But that's in the past. Where is the roller coaster headed in the future?

Well, there are two opposing forces at work.

The first is a negative force -- at least temporarily -- that arises from Microlog's $2 million acquisition of Genesis Electronics Corp. of California. As a result, Microlog recently said, it is expecting a significant increase in expenses, which could produce "substantial operating losses" this year.

The second force is a positive one.

A few days ago, Microlog made a deal with Racal Recorders Ltd. of Great Britain, which calls for Racal to market Microlog's voice-processing technology throughout Europe.

Under the agreement, Racal will pay Microlog what was called a "significant fee" for three years in a row. It also will set "annual minimum purchase targets" for the Microlog products that Racal will buy.

The two firms declined to say how much money Racal would pay Microlog in fees, or how many purchases would be made. But Racal acknowledged that it expected Microlog products to generate sales of almost $100 million within five years.

If Microlog were to get even a small slice of that pie, it could equal or double the $14.6 million in sales reported by Microlog for the fiscal year ending Oct. 31.

Those who have watched the voice-message business in this country grow from zero to $1 billion over a 10-year period think similar growth will take place in Europe. There are predictions that voice-message sales can grow to $800 million in Europe by 1994.

For Microlog, an important factor about the deal is that Racal is a company with deep pockets. Racal Recorders is one of the world's largest manufacturers and suppliers of professional recording equipment. The company, in turn, is a division of Racal Electronics PLC, which has worldwide sales of $3.25 billion.

What also is interesting about the Microlog-Racal deal is that it is the second time that a small U.S. voice-message company has teamed up with a large international company.

During the past several years, Hewlett-Packard Co. bought 10 percent of Octel Communications Corp. of California. Octel claims to have 22 percent of the voice-message market while AT&T has about 13 percent.

There is no suggestion that Racal may buy any of Microlog's stock. But the precedent is there. And strategic alliances are increasingly commonplace in competitive businesses.

At any rate, Microlog stock, which was selling in the $1.75 to $2 range for several months before the announcement of the Racal-Microlog deal, closed the week at $3.37 1/2, up from $2.25 a week earlier.

In his recent annual report, Chairman J.G. Hartwell observed that his company has a net worth of $4.83 a share and working capital of $4.17 a share. As a result, he said, the company plans to buy back up to $1 million of its common stock before mid-March.

Hartwell, who is 60, also said that, for health reasons, he will give up his job as chief executive. He has held the job since 1969, when he cofounded the company with Joe J. Lynn. The CEO's job will go to Lynn, who is the firm's president. Hartwell will remain as chairman.

Johnston, Lemon & Co. of Washington, once a major regional brokerage firm, continues to shrink. In recent months, the firm has closed its Alexandria and Bethesda offices.

Now, the firm has lost one of its veteran Greenbelt brokers, Edward F. McGehrin, who spent 30 years at J&L. He has moved to Merrill Lynch Inc. in downtown Washington.

Joining McGehrin in the move to Merrill was his son, Martin McGehrin, who spent eight years at J&L. Broker Joseph Wilson, their administrative assistant, went with them.

Ed McGehrin was reluctant to discuss the reasons for his departure after so many years, but apparently it involved strong disagreements within the firm.

Meanwhile, a number of J&L brokers recently joined Legg Mason Inc. in its Alexandria office. Veteran J&L broker Trewitt D. Harding has become the manager of Legg's Alexandria operation.

American Capital and Research Corp., which makes its home in Fairfax, will change its name to ICF International Inc., on March 1, the beginning of the firm's new fiscal year. The company's common stock will continue to trade on the Nasdaq National Market System but its ticker symbol will be changed to ICFIA.

American Capital and Research provides environmental, engineering and other professional services and turned in sales of $580 million in the last 12 months.

The company was originally founded in 1969 to help minority-owned businesses and was called the Inner City Fund. That's where the ICF comes from.

In the years that followed, the company expanded into professional and technical services and acquired a number of other companies that were renamed ICF this or that. So today you have ICF Kaiser Engineers of Oakland, Calif., and ICF Information Technology of Fairfax, and ICF Consulting Associates of Washington.

Chairman James O. Edwards said he thinks the company's current name is misleading, in view of its growing international business. The name, ICF International, will be more familiar to customers and shareholders, he said.

American Capital's shares moved up last week to $13.62 1/2 from $12.13, perhaps because of a report in ENR News, a construction industry publication, that ICF Kaiser Engineering may be one of the U.S. firms hired by Kuwait to participate in its $100 billion postwar rebuilding.

Legent Corp., the Vienna-based developer of software for IBM mainframe computers, is planning to sell 853,400 shares of stock that the company acquired under its buyback programs. The company expects to proceed with the sale as soon as it gets approval from the Securities and Exchange Commission, according to Richard Hanlon, the communications director.

The sale could pave the way for Legent to make some new acquisitions. The computer industry is continuing to consolidate and Legent, which has $90 million in cash and investments, is in a good position to buy smaller firms.

The best way for computer companies to buy other computer companies, Hanlon said, is to do a stock swap. In other words, Legent would say to a company it wanted to acquire, "We'll give you our stock for your stock."

However, the existence of the 853,400 shares being held by Legent could inhibit a possible acquisition, Hanlon said. The reason is that companies are not permitted to buy back their own stock at one price -- in this case about $20 a share -- and then use that stock in a swap when it is worth $36.50 a share.

So the answer is for Legent to unload the shares and add the $8.5 million profit to its already fat coffers.endquad