Perpetual American Bank, F.S.B., the Washington area's largest federally insured savings institution, ended its first full year as a public company with a sharp increase in earnings, the bank reported yesterday.

The improvement was caused by two major real estate transactions and its general business earnings, according to Thomas J. Owen, Perpetual's chairman.

For the fiscal year that ended Oct. 31, net interest and noninterest revenue increased 69.2 percent over last year, from $69.5 million to $177.6 million. Net income rose to $21.1 million ($2.95 a share) from a loss of $2 million, the bank said.

Net interest revenue increased because of better loan production and lower interest rates, which reduced the bank's cost of funds, Perpetual said. Noninterest revenue improved because of gains from real estate and mortgage-backed-securities sales and increased loan-fee and real estate venture income.

Assets as of Oct. 31 were $4.1 billion, up 14 percent from $3.6 billion the previous year. Deposits were $2.9 billion, a 21.8 percent increase from $2.4 billion in 1984.

Fourth-quarter revenue was $16.2 million, up from $8.5 million during the same period last year. Net income was $3.4 million (36 cents). The bank said it did not have comparable net income figures for the fourth quarter last year.

*Washington Homes Inc., a Waldorf-based builder, reported earnings for its first quarter that ended Oct. 31 of $1.5 million (83 cents a share), up 104.8 percent from $746,346 (41 cents) a year ago. Revenue was $18.7 million, up from $16.4 million.

*James River Corp., a Richmond-based paper company, yesterday reported a 5 percent decline in earnings for its second quarter that ended Oct. 27. Revenue increased 6 percent from $639.2 million a year earlier to $674.5 million. Net income decreased from $30.1 million (86 cents a share, fully diluted) to $28.6 million (79 cents).

Six-month revenue rose 3 percent to $1.304 billion from $1.264 billion. Net income slipped to $52.3 million ($1.47) from $52.5 million ($1.67).