It's a long, long way down the Top 100 list from Martin Marietta Corp., which sits grandly in first place, to Netword Inc., a small Maryland company that finds itself with an uncertain distinction: It's on the list -- but in 100th place.

Martin Marietta, an aerospace giant, earned its first-place ranking by ringing up $3.9 billion in sales last year. Netword, a struggling young company that delivers electronic mail via the U.S. Postal Service's E-COM system, squeaked into 100th place with revenue of precisely $629,320.

While Martin Marietta has 61,000 employes, Netword has a staff of seven. The seven include Diana Guetzkow, the 37-year-old president of Netword, and her husband, Daniel S. Guetzkow, 35, the firm's executive vice president.

Life at the bottom for the Guetzkows is, alternately, exhilarating, exhausting, challenging and frustrating. For them, the free enterprise system means knocking on doors to borrow start-up money; getting up at 3 a.m. to work on a proposal due that day; drinking carrot juice for lunch to fend off the burnout that comes from working 12-hour days, and living in a 1 1/2-bedroom house a short walk from the office to keep expenses low.

Netword serves clients who want to use the E-COM service. By arrangement with the Postal Service, Netword generates letters on its own computers and transmits them to post offices, whose letter carriers deliver the printed, Mailgram-like messages throughout the country.

Netword, whose fiscal year ends in January, has shown losses each year it's been in operation. But it saw its revenue rise from $32,000 in 1983 to $117,000 in 1984 to $398,00 in 1985. Meanwhile, the number of E-COM letters handled by the company has risen from 42,000 in 1983 to 277,000 in 1984 to a predicted 772,000 in 1985.

At one point, Netword had 20 employes. That was before June 5, 1984, the day near-disaster struck the 4-year-old company, when the Postal Service announced it planned to get rid of E-COM by selling or leasing the system. To the Guetzkows, it looked like they were out of business.

"I went into shock," Diana Guetzkow said. "I really did. I was devastated."

Netword's stock took a dive. The company's 3 million shares had sold for $1 each when the company went public in 1983, and had soared as high as $3 a share before leveling off to the $1.25 range. When the news broke, the price collapsed, and the stock has not recovered. The shares are now selling for 38 cents each.

Just a month before the Postal Service announcement, Diana Guetzkow recalled, Netword's prospects seemed bright. "We had just reached the point where we were being profitable. . . . And for the first time I thought, we're going to make it."

"It wasn't just that I wanted to make it for the pride, or for the financial reward. It wasn't that. I wanted the shareholders who had made that investment to have something to show for it. . . . I took it very personally."

As the shock wore off, the Guetzkows started thinking about what to do next. One possibility was to strike up a relationship with the company that bought E-COM. So far, nobody has. Another was to switch to selling a different product -- such as software for the UNIX computer operating system, promoted by AT&T, that Netword has been using for E-COM. Still another course was to acquire a firm that needed additional capital to become profitable.

Netword still has $2 million of the $2.5 million it netted from the the initial stock offering, and Diana Guetzkow is proud of her thriftiness. "It shows that we didn't have lavish dinners, unnecessary trips, great hotels, all of the perks that executives use."

Diana Guetzkow dislikes the idea of giving up on E-COM. "I have an emotional commitment to this and there's some point at which I'm going to have to say, 'That's that.' But I haven't reached that point yet."

Netword's president decided long ago that she felt "a call" to open her own business.

"I felt that my own talents and my confidence in my own abilities were such that I could do better in my own environment than in a large corporate structure. . . ," she explained.

"As a woman, I felt financially that I would do better. The risk was much greater, but the potential for reward was much greater than in the corporate ladder, where even though women have been doing better, everyone knows that women are not paid as well as men." In the beginning, the Guetzkows took no salary. Today they arepaid $50,000 each.

A child of Polish refugee parents, Diana Guetzkow arrived in this country at the age of 7, grew up in New York City and graduated from the City College of New York at 19 with a bachelor's degree in physics. Two years later, skipping a master's degree, she had her PhD in foreign policy from the City University of New York.

She spent two years as an analyst at the Department of Energy, where she got hooked on the subject of electronic message communication and processing. "This is the business to be in," she said she decided.

Five years ago, she met Dan Guetzkow in California. He had a background in engineering and computers and was running a plastics production plant. They had a whirlwind courtship and marriage -- all in one week. "It was right out of the movies. He was my dream. He had all of the characteristics I was looking for," she recalled.

Not long afterwards, at her urging, the Guetzkows started their own business. From then on, it was proxy statements at breakfast, balance sheets at dinner, and nothing but work, work, work -- Saturdays and Sundays included.

Some grim humor at the E. F. Hutton offices in the wake of the firm's guilty plea to charges that it defrauded its bankers: "If they haven't heard of Hutton before, they've heard of us now," anguished one broker. Hutton's New York officials quickly assured brokers that the firm would mount a major public relations campaign to try to overcome the black-eye effect of the episode. The news sent E. F. Hutton stock down $3.50 to close Thursday at $29 a share (although the stock gained $2.50 of that back on Friday). But Hutton brokers were quickly told by headquarters that they could not take advantage of the drop in price to buy stock for their own accounts until today.

Institutional Investor, ranking the nation's brokerage firms in its April issue, places Alex. Brown & Sons Inc. 40th in terms of total capital, with $56 million. That is a sharp fall from last year, when the Baltimore firm ranked 29th. Its Baltimore rival Legg Mason placed 56th with $37 million, up from its 86th spot last year. And Wheat, First Securities of Richmond, entered the list for the first time at 86th place with $21 million.

In terms of staff size, Wheat, First holds 22nd place with 557 brokers, Legg Mason ranks 38th with 335 brokers, and Alex. Brown is 41st with 318 brokers. By number of branches, Wheat, First ranks 16th with 53 offices, Legg Mason is 26th with 37 offices and Alex. Brown holds 42nd place with 19 offices.

Moody's Investor Service has boosted the rating of Potomac Electric Power Co. bonds to AAA from AA1, unusually high for a utility. Moody's also has raised the rating on Chesapeake & Potomac Telephone Co. of Maryland's debentures from A2 to Aa3.