It is said that Washington is a one-industry town, and that Uncle Sam is the chief industrialist. But private business in Washington is also a force to be reckoned with. While either retail nor wholesale business in the District is without problems, both are experiencing a boomlet. The following is the third in a series of seven portraits of people who are in private business in Washington.

Manuel V. Fernandez well recalls the beefy, bearded man. The scene was the kitchen of his father's restaurant. The place was Havana, Cuba. The time was World War Two. The night was most any.

"He would stick his head in and ask, 'What am I eating tonight?'" Fernandez recalled. The man: Ernest Hemingway. The answer? "I never told him. I was too busy peeling potatoes."

Fernandez would never duck such a question now. He depends too completely on good will, his own and that of his customers. He had left Havana far behind, and is now toughing it out on a small, out-of-the-way street in Southwest Washington.

There, right beside the Washington Channel, at 650 Water St. SW., Fernandez runs a two-story motel, the Channel Inn, and a mostly-sea food restaurant, Pier 7.

You will note that the motel is not named Sheraton or Ramada. Nor is the restaurant a McDonald's or a Stouffer's or a Hot Shoppes.It is the lack of affiliation that forces Fernandez to hustle to get and hustle to keep his customers.

But nonaffiliation is not the only apparent difficulty. Fernandez began just three years ago. His business is just south of, and somewhat dwarfed by the imposing and popular Hogate's and Flagship sea food restaurants. And it is a family operation, which in many cases means less than expert management.

Not here, Fernandez's wife, Alma, who runs the dining room, held a similar job at the Greenbriar in West Virginia, where they met 23 years ago. Jose Fernandez, Manuel's brother, runs the kitchen, and he, too, learned from their father. "One of us is always on the floor," says Fernandez. "We make sure we take care of the customers."

What Fernandez leaves unsaid, of course, is that those customers are in constant danger of choosing from dozens of Holiday Inns and scores of other expense-account restaurants. But the fact is, many haven't.

Drawing heavily on white-collar trade that needs to be in a government office in Southwest the next morning, the Channel Inn turned a profit in 1976 for the first time. Pier 7, right in the nautically-decorated lobby, did the same. The total gross for the year, Fernandez said, was about $2 million.

What Fernandez and his associates went through to get into the black - indeed, to open at all - might well be a feature film.

Poor boy from Cuba, born into restaurant business. Dreams of opening his own place some day. Politically aware father. Moves family out of Spain ahead of revolution in the '30s. Sends 19-year-old son to U.S. in 1949.

Young man works and studies with the greats: Waldorf-Asotria, Fontainebleau, Greenbriar. Amasses a little money. Opens restaurant in Tampa, Fla.

But hates it. Sells it. Moves to Washington in 1964 "because it has the highest liquor consumption in the country per capita."

Opens The Embers, a steakery and drinkery at 1200 19th St. NW. But longs for a motel-restaurant. Negotiates for land on the Southwest waterfront. Spends four years planning and building a $3 million structure. All set to open Dec. 15, 1972.

Three days before, the roof falls in. Literally.

A workman mishandles a propane gas tank. It explodes. The resulting fire lasts six hours. Damage totals $630,000.

"You can imagine what we felt like," Fernandez said. "We almost went bankrupt."

It was nearly a year before Fernandez and his five partners, three of them silent, could open. Even today, the red ties in the main entranceway of the motel are charred.

But the Channel Inn has been remarkably trouble-free since. Not once in three years has one of its rooms been burglarized, and only once has the night cashier been stuck up. "The law enforcement agencies have done a pretty good job," said Fernandez, 48, "and that's one reason I'm not afraid to make my livelihood in the District."

Fernandez does not understand the surrounding neighborhood in one respect, however. Although it is populous and relatively affluent, only ten per cent of Pier 7's lunches and 20 per cent of its dinners are served to locals, he estimates.

But Fernandez does not concede that the balance is heading for Hogate's or the Flagship instead. "I'm kind of like David fighting Golaith," he said. "But I can't worry about the other guy. Our location is good. The customers will find their way to your door if you serve them well."

Fernandez overcomes the nonaffiliation of his businesses with what he calls "the personal touch" and "a lot of hard work." He is shooting, he says, for "government and salesman business." His surveys show that they are 75 per cent of his trade, considerably higher than most other District hotels and motels.

Channel Inn rates range from $34 to $38 a night for a single. Dinners at Pier 7 range from about $4 to about $9. "We're competitive," Fernandez said. "We have to be."

One problem Fernandez does not have is parking. He is far enough from the nearby restaurant giants and room the apartment sprawlof Southwest that his customers can often park on the street. Only ten per cent of his motel check-ins arrive by car, Fernandez said, way below the averages of his competitors.

Fernandez is president of and major partner in Manglen Corp. The company that actually owns Channel Inn and Pier 7. Alan Glen, a financier, "fronted" much of the construction money. Another partner is Lawrence N. Brandt, a builder and developer of area apartment complexes, many in Northern Virginia.

Why the consortium did not locate outside the District might seem unclear, especially since Fernandez admits that there are handicaps to doing business in town. Among them are a minimum wage 50 cents an hour higher than Northern Virginia's and a vastly higher sales tax.

"I guess I feel a deep commitment to the city," Fernandez said. "The city could not go any lower than it was in the 1968 riots. There are opportunities in the city. It was a calculated decision."

Fernandez said, however, that Southwest is "clearly the forgotten business area of the city. It's a shame. I don't really understand why." But he is bullish enough to have planned a 50-room expansion of the Channel Inn, within two years.

Fernandez is one Washington businessman who has personal reasons for being positive about the city. "I lived through the problems in Spain in 1936 and I saw what was happening in Cuba in '47 and '48," he said. "Where else was there to run? You're not going to let the Nation's Capital die."