Soaring interest rate costs are beginning to have a significant adverse impact on the profitability of some corporations, according to early first-quarter reports yesterday by major Washington area firms.

Marriott Corp. earnings rose a modest 8 percent despite substantial gains in hotel and contract food service operations, while Federal National Mortgage Association said record interest rate levels on borrowing cut sharply into earnings.

Marriott, whose extensive restaurant operations suffered a decline in pretax profits, reported overall earnings in the period ended March 21 of $12.66 million compared with $11.77 million a year earlier. Per-share earnings rose 29 percent to 40 cents from 31 cents, a larger gain that reflects the company's purchases of 12.5 million shares in the past 16 months.

President J. W. Marriott Jr. said interest rate costs have doubled from a year ago due to financing of the stock repurchase program and the soaring interest rates. Sales of Marriott rose 16 percent to $350.4 million.

Revenues from Marriott hotel operations rose 25 percent and pretax profits were up 23 percent although occupancy rates -- in the 80 percent range -- showed a slight drop. Two new hotels opened during the quarter, in Houston and near Pittsburgh.

At restaurants, however, "customer counts remain soft, and costs have risen markedly" because of higher minimum wages and advertising and food costs, Marriott stated. Sales rose 11 percent but operating profits fell 12 percent.

Marriott said that "even if the economy does run into trouble," he expects 1980 to be a good year for the Bethesda-based firm. "Our restaurants overall may continue sluggish for a while longer but our lodging and other businesses should have good results for the year as a whole," he added.

Federal National Mortgage Association, a Washington company that supports a secondary market in home mortgages, said net income for the first quarter declined to $24 million (40 cents a share) from $39.5 million (65 cents) in the same period of 1979. Fnma's return on its mortgage portfolio was $25 million, compared with $64 million a year earlier.

"The lower return resulted from sharply increased borrowing costs that more than offset the increase in yield on Fannie Mae's portfolio," the government-chartered firm said. Commitments to buy mortgages totaled $2.3 billion in the first quarter compared with $1.4 billion a year ago.

United Virginia Bankshares, the largest banking firm in the state, reported first-quarter operating profits of $7.9 million ($1.47 a share), up 32 percent from $6 million ($1.11) in the 1979 period.

Chairman Joseph Jennings noted, however, that the strong gain partially reflects a reduced provision for loan losses related to discontinuing the business of a factoring subsidiary -- benefitting 1980 earnings by 29 cents a share, in comparison.

He said that despite strong loan demand, first-quarter profit growth was slowed by declining net interest margins as depositors shifted funds to higher-yielding investments. Average loan volume rose 16 percent to $2.17 billion. Average assets increased 6 percent to $3.19 billion.

Citizens Bank and Trust Co. of Maryland, based in Riverdale, said operating earnings rose 20 percent to $14.6 million compared with $12.2 million. Net income, adversely affected by rapidly increasing operating expendses, dipped to $1.94 million ($1.44 a share) from $2.3 million ($1.72).

Total resources increased 12 percent to $619 million and deposits were up 12 percent to $538 million. CB&T opened its 56th and 57th offices during the quarter, in Gaithersburg and Forestville.

First Federal Savings & Loan of Annapolis reported first quarter profits of $454,095 compared with $561,014 a year ago. Assets increased to $374 million from $345 million.

Solon Automated Services Inc., a nationwide operator of laundry equipment services based in D.C. reported earnings of $1.36 million (44 cents a share) in the first fiscal quarter ended Dec. 31 compared with $1.35 million (43 cents) a year ago. Sales rose to $17.6 million from $15.9 million.

Robertshaw Controls co., an instrument manufacturer in Richmond, said first-quarter profits rose to $3.19 million (82 cents a share) from $3.16 million (81 cents) a year ago as sales increased to $92.1 million from $82.6 million. The firm also reported a decline in incoming orders.