Raising $4 million was no problem when a new high-tech telecommunications company called Spectrum Microwave Corp. went public last May.

Spectrum, of Herndon, convinced a consortium of New York penny-stock underwriters to handle the offering. Two million shares of its stock were sold at $2 a share.

Earlier, the company's directors and their immediate families had bought the bulk of another 2.6 million shares in the company, founded only last February, for a penny a share. Shares offered to the public were heavily diluted, with a book value of only 77 cents a share, but that didn't dissuade investors.

Nor were investors deterred by the 22 caveats in the company's prospectus. For instance, the product -- telephone "bypass" technology -- isn't scheduled to exist until February, the need for additional financing is anticipated, the market is intensely competitive and established companies have more than a toehold.

"It's highly risky -- many of these companies go out of business -- but occasionally there are some fantastic winners," said Norman Fosback, editor of New Issues, an investment newsletter.

While institutional investors "generally avoid such offerings like the plague," Fosback said the offering was quite successful among private investors willing to take a risk when viewed against the backdrop of a slow spring, when many brokerage houses were cutting back on marketing new issues.

The company's stock is hovering at about $4.825, up from $2 a share, reports principal underwriter S. D. Cohn & Co.

Part of the offering's success is confidence in the new market for the so-called "bypass" technology the company will market. "This is going to be a viable technology, there isn't any question about it," said Brad Peery, an analyst with Hicks Peery, a San Fransisco investment firm.

Bypass technologies allow companies to construct their own communications networks that connect to long-distance facilities without hooking into the local telephone company. Bypassing lets companies avoid often lengthy local telephone company service delays and save money.

"If I am faced with a long-distance company that can solve the 3,000-mile problem and I'm faced with a local telephone company that either can't or won't, I'm going to do something about that," said John B. Mann, president of Spectrum.

If things go as planned, inside stockholders will convert their 57 percent ownership to 72 percent this spring by trading each of their Class B shares for two Class A shares.

Those inside stockholders include Mann, a former MCI corporate planner, and two other defecting MCI executives, Robert P. Bernardi, Spectrum's chairman, and Lee O. Horton, vice president of finance.

Another insider, Robert M. Sterling Jr., who is vice chairman, was formerly a securities broker with John Muir & Co., a New York brokerage house that went out of business in 1981. Muir was the lead underwriter for the first offering by Digital Switch Corp., now a very successful electronic telephone switch manufacturer that earns more than $300 million a year in revenue.

Although Sterling refuses to discuss the matter, the Securities and Exchange Commission in February ordered him not to work as a stockbroker for three years after finding he violated the federal securities act.

According to an SEC order, Sterling, while a broker with Muir, was instrumental in Muir's underwriting of an oil and gas company called Basic Earth Science Systems Inc. Basic netted $14.5 million from the 1980 offering, to be used for repayment of bank debts and for operations.

But Basic used part of the proceeds to buy about 135,000 shares of Digital Switch through Sterling, the SEC order says. The transaction wasn't reported to the SEC, though it should have been because of potential conflicts of interest between the underwriter and the issuer, according to the SEC.

Also, the SEC said, Sterling agreed to invest in a Basic-sponsored oil and gas drilling venture four days after Basic's initial offering; but Sterling didn't have the money for the investment, so he borrowed $70,000 from Basic. Once again, the SEC found Sterling's investment and loan from Basic should have been disclosed.

Spectrum plans to market one type of bypass technology, a microwave radio system that will transmit data, voice and video signals, said Mann. The company will also produce "multiplexers," computerized devices that plug into a number of bypass technologies to allocate different types of signals.

The bypass industry is expected to gross about $500 million this year, and is expected to grow to about $10 billion by 1994, according to TeleStrategies Inc., a telecommunications consulting firm. About a $100 million chunk of this year's gross belongs to microwave systems and multiplexers, industry sources report, and the number of bypassers is 1 in 4 and growing, according to Touche Ross & Co., a Washington consulting firm.

Spectrum is targeting the very companies who complain about bypassing: the local telephone companies determined to keep customers from leaving the rate base. "The telephone company would want to use our equipment because it's cost competitive and provides very quick service," Mann said.

Spectrum also will market to long-distance companies coming under pressure from users who want the service.

Among phone companies interested in providing the service is Bell Atlantic, which has a license to construct systems in the Norfolk/Richmond area and intends to blanket its region with the service. Long-distance companies such as MCI and GTE Sprint also are slated to provide it.

"We're right on schedule with our hiring," and product development is on target, he said. About the competition, which also includes Nippon Electric Corp., he said: "I think what we're going to do is get the jump on them, and we have to be careful they don't get the jump on us."

Mann contends that the company will produce a system with capabilities and features others don't have.

The big "unknowns" include whether Spectrum will be accepted by its target market, whether the company can withstand competition, whether regulators will allow local telephone companies free rein, and whether analysts' projections on the future of bypass will prove accurate. With a little luck on those fronts, Spectrum could strike it rich.