Washington's supercharged economy, cushioned by the highest income levels in the country and an ever-expanding government, is showing its first strains from the economic downturn affecting the rest of the nation.

In the last 30 days, stores, hotels, restaurants, banks, auto and boat dealers -- and one stalwart of the Washington area economy, the real estate industry -- have shown marked declines or sluggishness in business.

In addition, apartment managers have started to notice an increase in delinquencies by renters, and some banks have begun to slash their loan rates to help carry troubled commercial customers.

Together, these indicators have fostered a mood of apprehension that the recession is right around the corner and threatens to be more severe than in 1975.

"I think it's going to be a little tougher this time," says prominent real estate broker Foster Shannon. Adds Riggs commercial loan officer John Maupin: "We're all in this together."

Real estate sales, already dwindling since last fall, took their worst beating yet in March. "We've been counting sales since 1973, and this is the lowest March ever," said Deborah Rosenstein, senior researcher for Housing Data Reports.

New homes purchases in the metro area plummeted 57 percent for the month, according to the Housing Data survey, whose preliminary figures also showed a 71 percent decline in condominium sales.

Savings and loan institutions in the area recorded a 20 percent drop in total loans made in the first 60 days of this year, figures from the Federal Home Loan Bank show.

Yet, contradictions abound. Some businesses are still booming; in many ways, the city appears to be recession-resistant:

Wealthy Washington sailors are still buying 40-foot sloops with teak decks, spacious salons and $100,000 price tags, says a large Annapolis yacht broker.

Last month, an assortment of rich buyers and investors each put down $10,000 cash each to reserve a luxurious townhouse at Hillandale, Georgetown's newest address. All 26 of the $260,000-and-above units were snapped up within seven hours. Construction has not even begun.

While medium-priced restaurants are suffering, the two-martini lunch trade at high-priced restaurants along K Street and Wisconsin Avenue is as strong as ever.

Many people are still spending money.

"Inflation will only stop when people think they can buy it cheaper at a later date," said National Savings and Trust vice president John Bolton.

But there are strong signs that Washington is not the totally recession-proof fortress that many have believed.

David Hillman, general partner in one of the Washington area's largest apartment management companies, said that his rental delinquencies have tripled in recent months -- from 1 to 3 percent of the 10,000 units his Central Management Co. controls.

Moreover, a number of tenants who have given notice to move in the last two weeks have suddenly changed their minds -- deferring moving costs until later, he said, adding "We rarely get cancel notices."

To help commercial customers like auto dealers and builders withstand soaring credit charges on their inventories and projects, some banks have lowered their loan rates, voluntarily cutting their own profits.

"Before, we often loaned money at 2 (percent) over prime, but we're making some new loans at 1 of a half (percent) over prime," says Riggs' Maupin. "We want to keep our customers healthy. It's no use putting them out of business."

In a wave of corporate cost-cutting business travelers -- long fuel for the city's unique expense account economy -- have begun postponing and cancelling trips to Washington. Hotel occupancies at the 44 largest downtown hotels were off 12 percent in the first two months of the year, hotel association figures show.

"This is another precursor," said association president Ed MacMillan, manager of the international Inn on Thomas Circle. "Corporate executives are the grease that oils the economy. A reduction in business travel usually starts before the rest. I've seen it before, it was the same in 1975. Within 90 days, we'll start reading about the drop in retail sales and unemployment going up. I hope I'm wrong."

The figures suggest he may be right.

After President Carter slapped credit controls on American consumers March 14, Washington area shoppers began to show the first signs of caution, keeping hands off wallets and credit cards. Sales in downtown stores declined modestly in March, reported the Greater Washington Board of Trade, while suburban stores posted only a slight increase.

Even the proprietress of a large outcall massage service that caters to Washington's executive visitors reported that customers are drinking more, dallying less and keeping unusually quiet about how things are at the office."During good times, they can't wait to tell you how many big deals they've made," she said.

The District's unemployment figures were still holding steady through February at 6.5 percent. However, in the metropolitan area, total jobs decreased by 2,800.

Among the worst hit were the area's teen-agers -- almost four out of 10 can't find jobs. Those Depression-era levels of unemployment are even worse among the District's teen-age black males: half are out of work.

And, for the foreseeable future, consumers plan to dramatically cut back on their vacation travel plans, according to a March 23 Gallup Poll commissioned by the National Restaurant Association.

Washington restaurant association spokesman Jack Cockrell said that in the last two weeks of March, the area's $800 million annual restaurant trade dropped off noticeably. He said that the vast majority of restaurants -- the ones in the middle price range -- traditionally suffer the effects of recession first.

A detailed breakdown of the Gallup Poll results carries an ominous message for remote resorts, hotels and restaurants. More than half of those polled said that high gasoline prices would definitely affect their vacation plans. Of those, one in three said they would cancel vacation plans altogether.

One large Washington caterer, Jeff Ellis, president of Ridgewell's, has his own method of divining the economic tea leaves: he examines his client's orders. "To my clients, a party is business," he says. "They are people who have money and are always going to spend money.

"They still entertain elegantly," he added, "but not they don't order whole jumbo shrimp, they order shrimp salad. It costs less, but it's still shrimp."

For some, the signs of impending recession have been clear for months.

Foster Shannon, partner in one of the area's largest real estate brokerage firms, Shannon and Luchs, says he has spotted a downturn coming five times in his 30-year career. A year ago, he was certain he saw it coming again. "Real estate just can't keep going sky high forever," he believed. "Pretty soon you'd be paying $900,000 for a one-bedroom (apartment)."

So last summer, Shannon, a multimillionaire, quit the board of directors of the National Bank of Washington midway in his sixth year to guide his firm through the coming crunch.

He was still waiting last week -- somewhat befuddled -- for something to happen. The latest dispatches from the firm's branch offices sounded like this: Wisconsin Avenue branch, a robust $3 million in March sales and only three contracts in doubt; the Wheaton branch, a strong $2.7 million in sales on 29 contracts.

"I'm beating last year's figures, but all of the signs tell me I shouldn't be," he said.

In his office overlooking Farragut Square, he keeps a set of leather-bound company books from another era -- the Depression. "You know, my Dad lost everything he had," said Shannon of his carpenter father, firm cofounder Herbert T. Shannon. But the business reovered and several years ago, Foster Shannon retrieved the books from storage.

"I keep them there as a constant reminder. Every time I think of borrowing another $100,000, I look over at those books."

Others, newer to the real estate game, have had no reminder. Smaller brokerage firms, less insulated than Shannon and Luchs, along with developers like Holland and Lyons, who found themselves overextended in a becalmed market, have cut back dramatically. Many agents are looking for steadier work.

Speculators and investors who bought up properties with short-term notes on the assurance that the market would always provide a steady stream of buyers, face burdensome carrying costs and a market with far fewer buyers. Some fear the collapse of their paper pyramids.

Already, real estate sharks -- speculators armed with cash and tough terms -- are desperate sellers. Says one speculator, who liquidated his properties last year and now sits on a comfortable mountain of cash: "I always find a little joy in the despair of others."

The last downturn Shannon saw was in 1975, when interest rates hit 14 percent and his $500 million company posted a total profit of $7,500. "That was the proudest $7,500 I ever made," he said.

A sudden drop off in total Washington Post classified ad lines in March was attributed to sharp declines in two categories: auto sale ads and local employment ads. Classified ad manager Louis Limber said that the 5 percent drop during the month was the first such decline in three or four years.

"We've had all-time highs in classified sales for the last three years in a row," Limber said. "This is something we're just not used to."

Some area auto dealers said they have watched helplessly as tight credit and soaring loan rates have chased their customers away. In some cases, sales have collapsed 50 percent below last year's figures.

Annapolis boat dealers are also feeling the impact of credit restrictions on spring boat sales. Only half as many customers seeking boats under $60,000 are qualifying for loans, says Alan Hamerstrom, owner of Inter Yacht Inc. in Annapolis. Banks are "extremely reluctant" to lend money to small boat buyers, he said. "Small dealers are going to be severely hurt.

"We're certainly not hit as hard as the auto dealers, but we're hit pretty hard," he said.

Stereo sales in February-March for Circuit City which has six outlets in the Washington area, were "about 12 percent ahead of last year," said Dan Rexinger, senior vice president for Richmond-based Wards Company, which owns the stereo chain. "We're very nervous about the future, but we haven't started feeling (the recession) yet."

But Myer-Emco's Jim Zeiger, manager of the electronic firm's Washington store at 18th and M Streets NW, notes a softening in sales, largely due to a decline in credit card purchases. Customers are shopping around longer before buying, he says, and when they buy, they often pick up one piece of equipment, rather than a whole system.

"Spur-of-the-moment purchases are fewer and farther between," he says. Once easy-spending customers are reigning in their "gotta-have-it" impulses.

Nevertheless, curious pockets of strength remain.

Of the almost instant sellout of his $260,000 Georgetown townhouses. Michael Gulino, vice president of Hillandale Development Corp., says, "It may be possible that there is an inflation-proof factor at certain price levels." But in another part of Georgetown, just a mile or so away, real estate agent Judy Frieder can't figure out why four condominiums that went on the market a month and a half ago at $160,000 to $210,000 are still sitting vacant.

Why? "Price," she said. "They're very expensive." At $200 and more per square foot, the apartments are among the all-time highest-priced in the city.

Many real estate agents, accustomed to a decade of dizzying appreciation, constant turnover, speculation and easy sales, are working longer hours and scoring less often. To cut costs, broker Ed Henry moved his 10 agents from chic M Street offices to the relatively drab landscape of 11th Street.

Henry's advice: "You'd better have a rich uncle who has a lot of cash he wants to give you as a gift if you want to buy anything in town. Anything with owner financing is selling, but just about everything that needs new financing is sitting -- and we don't know for how long.

"There is major despair on the part of homeowners who would like to sell and can't find buyers, and among buyers who would like to buy but can't qualify for loans," he said.

"If it (the market) isn't dead, it's very close to it," said builder and bank director Jeffrey N. Cohen.

"Home loans are practically nonexistent," says National Savings and Trust vice president Bolton. But, he added, "The way things are changing from day to day, you think you know what's going on and then the next day you think you're crazy."

Many of those still able to play the Washington real estate game -- without high-priced money from a friendly banker -- are buyers who have cash and sellers who are willing to take back a note for a big chunk of their property. At a recent settlement on a $200,000 townhouse, a well-heeled couple sat around a table at District-Realty Title Insurance Corp. and commiserated with company president Samuel R. Gillman about high interest rates and tight money.

Satisfied that their contract to buy was in order, the wife fished a checkbook from her purse, turned to her husband and asked, "Should I take it (the $200,000) out of my checking account or are you going to take it out of yours?"

Others who have to borrow are finding money available -- at astronomical rates.Indeed, some bankers say they have plenty of money to lend, even though they are complying with the Federal Reserve Board's request to limit loan growth to 9 percent.

"A lot of companies would like to borrow money, but they feel morally opposed to paying such high interest rates," says Maupin of Riggs. "So we're not trying to push our money; we're pushing our relationships (for the future)."

Economic observers in some other cities that have felt the crunch earlier and harder than Washington look to the capital's looming tough times with relative envy.

"Philadelphia is having much more difficult times (than Washington)," says Harmon Spolan, president of Philadelphia's Jefferson Bank and a director of Rockville's State National Bank. Several large employers -- two tire companies, an auto plant, among them -- have laid off several thousand workers. The city has eliminated 1,200 jobs and laid off 700 police and firemen, he says. "Construction is at a standstill."

"We're feeling it at the bank," says Spolan, whose normal 2 percent rate of consumer loan delinquency (those that are 60-90 days late) has more than tripled. "People are asking us to let them stretch out their payments so they can manage.

"'Look,' they say, 'I can't make my car payment this month, can I pay next month?'"

Many of his commercial customers -- suppliers who sell to major retailers like Sears, J.C. Penny, Woolworth's -- are waiting, in some cases, up to 120 days to be paid. "Some big guys are leaning on the little guys," he says. 1"So the little guys come to us and say, 'All we can afford to pay is interest, which is 20 percent, can I defer the principal? That's not happening in D.C."

Indeed, while residential construction in D.C. has virtually halted, commercial builders -- still feeding an unrelenting demand for Washington office space -- have crowded the skyline with construction cranes. An official with Washington's building trades council, John Quackenbush, representing 25,000 area hard hats, projected heavy workloads and full employment for his men through the end of the year.

But after that, he added, "The whole thing could collapse" because many commercial builders are postponing projects now on the drawing boards.