First-quarter profits rose 14.1 percent at Riggs National Corp., parent firm of D.C.'s largest bank, Riggs National Bank, officials said yesterday.

The company earned $7.1 million ($1.19 a share) compared with $6.3 million ($1.05) in the first quarter of 1982. The gains were attributed to increases in noninterest income.

Riggs's reserve for loan losses has increased to $19.95 million from $16.3 million at this time last year. Nonperforming assets have declined to $33.5 million. The bank's assets are $3.74 billion, compared with $3.66 billion last year.

Marriott Corp., the hotel and restaurant chain, had a 14 percent gain in net income in its first quarter ended March 25, to $19.24 million (70 cents a share) on sales of $635.04 million, compared with net income of $16.94 million (63 cents) a year ago on sales of $516.21 million.

President J. W. Marriott Jr. said profits from the company's hotels, contract food services and restaurants were ahead of last year's first quarter, excluding the impact of dispositions and the transfer of five hotels to a syndication.

The dispositions included the Farrell's division and company's interest in a Denver hotel. The Bethesda-based company added 15 hotels and expanded six during the past year.

Suburban Bancorp of Bethesda said yesterday that earnings in the first quarter increased 6.7 percent to $4.9 million ($1.02 a share) from $4.6 million (96 cents) the year before.

Chairman Robert F. Tardio said a $1.8 million increase in fee income was responsible for much of the first-quarter gains. Total assets of the bank holding company are $2.1 billion, up 24.4 percent from $1.7 billion last year.