Riggs National Bank is still the biggest in town and its deposits are the fastest growing, but American Security Corp. made more money last year.

Posting the largest dollar increase in income in its history, American Security reported earnings of $17.5 million ($7.24 a share), up 10 per cent from $15.91 million ($6.59) in 1976.[TEXT OMITTED FROM SOURCE] to $15.2 million ($5.04), compared with $13.2 million ($4.36) last year.

Riggs deposits increased 18.9 per cent to a new record of $1.7 million and its total assets passed the $2 billion mark by $69 million. American Security's deposits were up 13 per cent to $1.3 billion.

Both big banks said increases in loan demand last year were major factors in their growth.

American Security ranked among the top five major banks in the country in return on assets and equity in industry surveys last year and will probably make that list again, the company said.

For the fourth quarter American Security's net income dropped, from $4.6 million ($1.94 a share) to $4.4 million ($1.83).

Riggs' fourth quarter net increased 16 per cent, from $3.8 million or $1.28 per share to $4.5 million or $1.49 per share.

Suburban Bancorp., the holding company that owns Suburban Trust Co. in Hyattsville, and the Thurmond Bank, reported a 7.7 per cent increase in net income to $11.1 million ($2.55 a share), compared with $10.3 million ($2.37) last year.

Suburban said its deposits grew by $150 million last year and assets increased $162 million to $1.090 billion. Fourth quarter income grew from $2.9 million (66 cents) to $3.1 million (71 cents).

Riding the crest of the housing boom that boosted its sales by 30 per cent last year to $116 million, The Ryland Group reported a 17 per cent increase in profits to $5.5 million ($2.12 a share).

A major homebuilder in the Washington and Baltimore areas, Ryland had sales of $89 million and earnings of $4.8 million ($1.80) in 1976.

Ryland said its backlog of contracts - houses sold but not yet settled - increased 58 per cent to $61 million.

Chairman James P. Ryan said shortages of insulation, drywall and labor resulted in increased building time and increased costs, preventing profits from growing as fast as sales.

New Virginia Bancrop. of Springfield said its earnings rose 17.7 per cent to $1.37 million ($1.17 a share), compared with $1.16 million (99 cents) the previous year.

New Virginia's deposits increased 13.4 per cent to $131 million and assets were up 12.9 per cent to $142 million.

Dominion Bankshares reported an increase in yearly profits to $13.66 million ($2.11 a share), up from $13.21 ($2.09) in 1976.

The Virginia bank holding company said its income before securities transations reached $13.83 million, a recor* d and 7.4 per cent above 1976.

During 1977 the 11 Dominion Bankshares banks increased their loans from $850 million to $1.03 billion, assets grew 8.4 per cent, from $1.55 billion to $1.68 billion, while deposits grew 9.2 per cent to $1.44 billion.

For the fourth quarter, Dominion earned 61 cents a share, up 15 per cent from the same quarter of 1976.

Byron. A. Hicks, president, said strong loan demand was the main factor in the earnings growth. He noted that profits for the last three quarters increased at an accelerating rate, indicating a positive trend for 1978.

Dominion Bankshares owns 11 Virginia banks, including Dominion Naitonal, and three bank-related companies, with a total of 122 offices in Virginia.

Avemco Corp. of Bethesda reported that 1977 earnings climbed 26 per cent to $2.6 million (94 cents a share), compared with $2.07 million (70 cents) last year.

Chairman Arnold Johnson said the profits were the highest in the 17-year history of the firm, which provides insurance and financing for general aviation aircraft.

He noted that annual earnings were boosted to record levels by "an extremely profitable" fourth quarter in which Avemco earned $950,000 (37 cents).

Avemco's insurance premiums for the year increased from $15.2 million to $16.9 million, less reinsurance, and net revenues increased from $13.4 million to $14.2 million.

Johnson said Avemco would pay a quarterly dividend of 7.5 cents a share in 1978, compared with an annual divident of 7.5 cents a share which has been paid since 1975.

Central National Bank of Maryland said its 1977 profits rose 22 per cent. The bank also declared both cash and stock dividends.

The 21 cent cash payout raises the bank's annual dividend to 33 cents a share from 22 cents in 1976. The 5 per cent stock dividend compares with 4 per cent in prior years.

The Silver Spring bank said its assets increased last year by 15 per cent, from $37.7 million to $43.3 million.

Central National's income before securities transactions increased 16 per cent to $278,000 ($1.53 a share) and not income climbed by 22 per cent to $304,000 ($1.67).

First Financial of Virginia, the parent company of Washington-Lee Savings and Loan Association, reported a sharp gain in profits to $1.001 million ($2.11 a share) for the six months ended Dec. 31, compared with $739,000 ($1.56) for the same period a year earlier.

As a result of the 35 per cent increase in earnings for the first half of fiscal 1978, First Financial raised its semi-annual dividend from 15 to 25 cents a share, president Richard S. Lawton said.

Equitable Bancorp. yesterday reported a 16 per cent increase in its 1977 profits before security transactions to $10.84 million ($3.10 a share), the highest in its history, compared with $9.39 million ($2.67) a year earlier.

"Continued strong deposit growth, higher loan demand and improved loan yields are among the significant reasons for increased earnings," Owen Daly II, chairman, said.

Fourth quarter profits climbed 23 per cent to $2.9 million (84 cents) compared with $2.4 million (68 cents) for the same period a year ago, the company said. Average loans increased 24 per cent to $998.6 million, principally in the commercial and real estate portfolios. Total deposits climbed 12 per cent to an average $1.36 billion for the year from an average $1.22 billion for 1976.