When Harold T. Judd left New Hampshire last fall to take a temporary job here as a lawyer, he and his friend Mary Walz bought a $78,000, brick colonial house in Silver Spring before they had been in town 24 hours.

"Renting is just not an option," Judd said. "Until they change the tax laws, you have to buy." When they leave town in a year or two, Judd said, they'll sell.

Washington, swept by tides of white-collar and military transients, has traditionally been an area where rentals outpaced home ownership. But now that is changing dramatically.

There were 130,000 more homeowners in the Washington area in 1977 than in 1970 -- a period when the population rose less than 4 percent.

And fresh U.S. census figures show that the surge in home ownership -- both condominiums and traditional single-family or attached homes -- during the 1970s pushed the proportion of owner-occupied dwellings over the halfway mark for the first time in Washington.

According to the census, nearly 52 percent of the Washington area's 1.1 million households were owner-occupants in 1977, the last year the data covers. In 1970, the figure was 46 percent; in 1940, it was 38 percent.

Young couples in their 20s, like Judd and Walz, probably would have rented an apartment in earlier years, experts say. But now the interplay of inflation, high salaries and the federal income-tax structure is making people particularly conscious of the advantages of owning a home.

The increase in ownership comes at a time of high construction costs, condominium conversions and rent controls -- all of which have created a squeeze on renters as apartments become costlier, more rundown and harder to find.

Experts see the increase in home ownership here as mostly a good thing -- with some drawbacks.

"It leads to more stable neighborhoods and a higher sense of community participation," said Louis Winnick, a Ford Foundation housing and urban economist. "Also it has proved, in our lifetimes, to be the best path for people of modest means to obtain a stake in life."

But George Grier, a consultant who has studied the Washington area's housing patterns, said there are "some negatives" to increasing home ownership: "It [becomes] harder for people to come into the area and to move on when jobs do or should disappear. . . In the long run, an area without a sufficient supply of rental housing may lose vitality."

In the District of Columbia, Susan, a 28-year-old lawyer with a $33,000 salary who asked that her real name not be used, bought a condominium.

"I was getting raped by taxes," she said. "I feel I have a responsibility to pay them, but it seemed that so much of my money was going to taxes it wasn't quite fair."

Tax experts said a typical Washington-area couple with one child and a $30,000 joint income could save about $1,300 in federal and $350 in state income taxes in the first year after buying a $75,000 house and placing a $65,000 mortgage on it at an interest rate of 10 and three-eighths percent.

The home purchase would enable the couple to deduct about $6,700 in interest and about $1,000 in real estate taxes on their income tax forms.

"I said I wanted a house before I was 25," said 24-year-old Debbie Johnson, as she sat in the kitchen of the $66,000 town house that she and her husband Gary bought in Springfield last fall.

Her husband said, "We got very, very excited about the prospects of the investment."

Home ownership here is growing faster than in most other metropolitan areas in the nation, although the proportion of owners still lags behind the 61 percent national average for other metropolitan areas.

Generally, home ownership here is about the same as in San Francisco, above New York City, and below cities such as Baltimore, Philadelphia, Fort Lauderdale and Seattle.

Housing experts say the spurt of ownership here is a sign that the Washington area is settling down from the boom decade of the '60s. The area's population rose 38 percent then as the size of the federal government expanded sharply.

The area's population rose just 4 percent from 1970 to 1975, and since then it has dropped slightly.

During the '60s, home ownership here declined as a proportion of all households while rentals shot up to accommodate the population influx. There was a 173,000 increase in the number of units rented during the 60s, but an increase of only 23,000 during the '70s.

In contrast, ownership increased strongly by 108,000 units during the '60s, even though it lost ground proportionately to rentals during that decade. Then, during the last decade, home ownership shot up by 130,000 units while rentals slumped.

That strong increase in ownership in the last decade continues a trend that has been prevalent here and nationally, at least since 1940.

In that context, the slight decline in ownership during the 1960s seems like a brief aberration.

Census and other data also show that:

Ownership in the District in 1977 was lower (32 percent of all house-holds) than in the suburbs (58 percent). The actual number of units owned increased only 10 percent in the city during the first seven years of the decade, while rising 36 percent in the suburbs.

Ownership among blacks in the area by 1977 was lower (34 percent of all black households) than for the population as a whole, even though the actual number of units owned by blacks increased at a sharper rate (46 percent) than it did for the population as whole (32 percent).

Black rentals in the suburbs increased so sharply that ownership among blacks there decreased from 46 percent to 40 percent of all black households during the decade. The actual number of black households in the suburbs, however, soared by 125 percent to 42,200 by 1977.

Owner-occupied condominium and cooperative units increased from 7,500 units in the area in 1970 to 38,800 in 1977 -- a twofold increaase in the city and a tenfold increase in the suburbs.

There are about 69,900 condominium units in the area now, half of them the result of conversions from apartments, experts suggest.

Raymond J. Howar, past president of the Washington Board of Realtors, called the increasing home ownership "a very healthy trend. Washington for too many years had too high a percentage of renters."

Howar said that the increasing ownership trend will bring in more local tax revenue because houses and condominium buildings are assessed higher than apartment buildings, where the value of the building depends largely on the amount of rent it can bring in.

Several analysts said that inflation has driven up building costs to the point where rental units are not being built because the rents would have to be set unacceptably high in order to give good return on investment.

Thus, the percentage of rental building starts in the area fell from 49 percent of all building starts in 1967 to 17 percent last year -- and a good portion of that 17 percent are condominiums destined to be owner-occupied.

"Because of the rent control laws [and] the increasing cost of construction, there are basically no new rental units being built," said local developer Alan Kay.

While the availability or rental housing tightens, the baby-boom generation born from 1945 to 1955 has reached the home-buying age. And incomes in Washington -- the product of high government and private industry salaries and an increase in double-income families -- are higher than most other places in the country.

"Once they get up to $20,000 or $30,000 income they want to get into a house," said Morton Schussheim, a senior specialist in housing at the Congressional Research Service. ". . . I'm sure there are a lot of people who would prefer to be renters if you got the same tax advantage and if you didn't anticipate inflation in real estate."

For many people like Judd, the 28-yer-old who just moved here from New Hampshire, home ownership appears to be a key element of personal financial and investment planning.

"I don't expect to be here more than two years," he said. "The reason for buying [a house] was purely financial."