Symbolic of new membership in the billion-dollar business club, Suburban Bancorporation yesterday staged its first annual meeting outside the cramped quarters of Suburban Trust Co.'s board room in Hyattsville.

A record turnout of more than 300 stockholders showed up at the Holiday Inn in Bethesda to hear company officers describe a systematic approach to increased business and profits in the suburbs.

Founded in Prince George's County in 1915 - when the first Suburban Trust office was surrounded by small villages and farmland - the banking company has grown with the Washington suburbs.

Its primary subsidiary, Suburban Trust, is the fourth largest bank in Maryland, holding some 30 percent of all commercial bank deposits in Montgomery and Prince George's counties.

Bancorporation President Robert Tardio noted yesterday that his firm currently ranks as 162d largest in the American banking business but is 106th in total profits, with a return on average assets that exceeds the 44 largest firms.

Tardio, who later yesterday was given the additional position of board chairman, told stockholders that Suburban's expansion of business last year, when assets rose by 17.5 percent to top $1 billion for the first time, reflected a significant shift in American life that is being demonstrated in the Washington suburbs.

No longer was suburbs just a place to live, with residents commuting to jobs. Now, "vast populations - particularly affluent ones - work, learn, shop and reside near older cities . . . banking needs for suburban communities like Silver Spring, Bethesda, Laurel, Greenbelt, Rockville and College Park have directed and shaped the scope of our services," he said.

And the profits from serving these growing communities have never been greater. Last year, Suburban Bancorporation earned a record $11.15 million compared with $10.35 million in 1976.

During the first quarter of this year, earnings growth accelerated to 19 percent. Tardio told the meeting. Operating profits were $2.86 million (65 cents a share) compared with $2.40 million (55 cents) in the same period last year.

Tardio attribued the strong first-quarter gain to higher interest income from a loan volume that was up 14.5 percent from the same quarter in 1977. Deposits rose nearly 11 percent to $959 million, and assets were up 13 percent to $1.09 billion.

Suburban Bancorporation owns Suburban Trust, which has 61 offices in the Washington and Baltimore areas; Thurmont Bank, with four offices in north-central Maryland; and recently acquired the Peoples Bank of Hancock, with two offices in Western Maryland.

The People acquisition, effective April 1, provides an exchange of 3.5 Suburban shares for each of the 20,000 shares of Peoples stock. The Hancock bank has assets of $11 million.

Tardio said another proposed Suburban acquisition - that of Free State Bank and Trust of Potomac - will be filed with regulatory agencies later this month. If approved, Free State would come under Suburban ownership in mid-July, with an exchange of 1.5 Suburban shares for each of the 100,000 Free State shares outstanding.

On other subjects, Tardio and Suburban Trust Chairman William Wheeler said:

They Hyattsville bank will open two new branches this year and new buildings for two existing offices. Negotiations are in progress for the sale of STC's Upper Marlboro office, which will be replaced by a new structure across from the county office building there.

In a pilot program with the Southland Corp., owner of the 7-Eleven convenience food stores STC has opened two automated teller facilities in 7-Elevens at 6435 Landover Rd. and 17701 Muncaster Mill Rd. The bank has 17 similar automated teller machines at its own branches.

Chairman Joseph Richards Jr. told stockholders that the board is "always" working toward increasing the firm's dividends and that Suburban lawyers have found no "merit" in a lawsuit by a shopping center developer in Baltimore County alleging breach of contract and fraud and seeking multi-million-dollar damages from STC and a Baltimore bank.

Following the stockholders' meeting, Tardio was elected to succeed Richards as chairman of the holding company. Richards will continue as vice chairman of STC and a member of the board and executive committee of Suburban Bancorporation.