High interest rates, tight credit and heavy demand for student loans pushed Student Loan Marketing Association to a 91-percent increase in profits for 1981, a record $18 million ($18.05 a share), compared with $9.4 million ($9.44) in 1980.

Sallie Mae said yesterday its fourth-quarter net income was up 89 percent, to a record $5.4 million ($5.42) compared with $2.9 million ($2.87) in the final period of 1980.

Regional banks also reported favorable results for 1981. Dominion Bankshares Corp., a Roanoke holding company that operates 13 banks and five bank-related affiliates, reported net income for the year was $21.9 million ($2.52 a share) compared with $20.2 million ($2.37) in the 12 months ended Dec. 31, 1980.

Fourth-quarter net income totaled $5.9 million (67 cents) compared with $5.1 million (60 cents) a year ago. For 1981, the company reported its assets were $2,731,681, compared with $2,525,876 in 1980, an 8.1 percent increase. For the same periods, deposits grew to $2,138,018 from $2,009,528.

In the District, Women's National Bank reported net income for 1981 was $240,345 ($2.40 a share) an increase of 36 percent, compared with $177,000 ($1.77) in 1980. As of Dec. 31, Women's assets were $16,530 and deposits were $11,847.

First Maryland Bancorp of Baltimore said net income in the fourth quarter was $6.4 million ($1.25 a share) compared with $5.5 million ($1.05) in the similar period a year ago. For the year, First Maryland reported net income of $23.6 million ($4.55) compared with $21.6 million ($4.13).

Computer Data Systems Inc., a professional services and data processing company based in Bethesda, said net income for the six months ended Dec. 31 rose to $552,500 (76 cents) from $525,500 (72 cents) as revenues increased 29 percent to $10.8 million.