An international business executive has quietly purchased enough shares of Riggs National Bank stock in the past two years to become the major stockholder of the metropolitan area's largest financial institution.

But the businessman, Jorge E. Carnicero, insisted in an interview that he has no intention of directing the bank's management from his new ownership position.

Carnicero, chairman of McLean-based Dynalectron Corp., also denied reports that he is representing outside banking interests in the Riggs purchases, although one investor associated with his Riggs stock purchases does have a banking business overseas.

Under laws affecting national banks, moreover, cumulative voting is required for directors -- allowing individual stockholders to concerntrate all their votes for the election of specific candidates rather than dividing votes for a management slate.

As the owner of one-tenth of the outstanding common shares of Riggs, Carnicero thus may elect 2 of the bank's 25 directors at this year's annual meeting in March. He has selected for the board his 30-year-old daughter, Jacqueline Carnicero Duchange, and a long-time business associate at Dynalectron, Merlon F. Richards, according to information supplied to federal regulators and scheduled to be made public in proxy statements later this week.

Jacqueline Carnicero would become perhaps the youngest person and the second woman to serve on the Riggs board. Margaret Truman Daniel joined the Riggs board in 1977, at the same time Jorge Carnicero became a director. Richards is executive vice president and chief operating officer at Dynalectron.

Founded as an exchange and brokerage house in 1836, Riggs was successor to assets of the Second Bank of the U.S., which was disbanded that year as the country's central bank. It long has been the largest bank in the nation's capital with current assets exceeding $2.4 billion.

Some of the Riggs shares were purchased by Carnicero with money borrowed at a major U.S. bank -- not in the Washington area -- with a line of credit ranging up to $1.8 million. Riggs stock is being held as collateral for these loans.

According to information filed with federal bank regulators, Carnicero or business ventures with which he has ties now own more than 252,000 shares of Riggs common stock -- about 10 percent of the shares outstanding and several times the holdings of the next largest owner.

Although Carnicero has owned shares of the bank for more than 15 years, the amount owned directly or indirectly early in 1977 was only about 37,000 shares. Most of his shares have been accumulated in the past 8 months.

Carnicero has told government regulators that, depending on market conditions, he may continue to buy stock of Riggs from time to time. But, in the interview, the Dynalectron official emphasized that he doesn't want to own so many shares that he would have to be designated as the controlling interest.

Under Federal Reserve Board regulations, any company or individual with 25 percent or more ownership of a bank must be declared a bank holding company. Shares of ownership ranging from 5 percent to 25 percent may be declared by the central bank to represent a controlling interest if the investor becomes involved in management decisions or close ties are evident through common directorships and other business developments.

Carnicero said his only interest in Riggs is as an investment and he has "no intention" of getting involved in management.

"My ego is really deflated," said Carnicero, when asked about local business community speculation that his investment in Riggs may be the opening wedge of a takeover attempt by outsiders. "To reach this age with a record of accomplishment and be accused of being a front man is sad," added the 57-year-old native of Argentina, who has been a U.S. citizen since 1950.

"Banking is not my business, I don't have the mentality," Carnicero declared. He said "nothing has been forced upon the bank" and that relations with other directors and bank Chairman Vincent C. Burke Jr. "couldn't be better."

Burke, in a telephone interview yesterday from New York, where he is attending a bank conference, declined to comment on the situation until proxy statements are sent to stockholders later this week.

Carnicero has made his investments as follows: 200 shares in his own name; 3,250 shares as trustee for his wife; 3,250 shares as trustee for his son; 239,246 shares owned by FinAmerica Corp., a Delaware investment company of which Carnicero owns a majority interest; 3,520 shares owned by Dynalectron pension funds, over which he has no direct control; and 3,300 shares by Estevez Boero, for which he has only voting rights and no direct interest.

There is no significant banking relationship between Dynalectron and Riggs although a Dynalectron subsidiary has maintained a nominal checking account at the bank for many years and the Riggs trust department long has handled investments for two Dynalectron pension funds.

Dynalectron currently is engaged in engineering, contracting and technical services, and has annual revenues of $330 million. Carnicero owns about 10 percent of Dyanlectron stock and considers the McLean firm the centerpiece of his business activities.

In addition, Carnicero is an officer or director of several international companies, with major projects including airplane leasing and real estate development in Latin America. A Delaware firm of which he is the sole owner, Trans-American Aeronautical Corp., owns a majority of FinAmerica -- the company with heavy investments in Riggs.

According to Carnicero, other owners of FinAmerica are private investors, including a "very large group" engaged in raising cattle, manufacturing and banking.

Ownership of Riggs has been widely spread out among area investors -- mainly through issues of new stock as other banks have been acquired over the years. The largest owners in recent years have been members of the Camalier, Corby, Fitzgerald and Davis families.

Like many other bank stocks, Riggs has been trading below its book value of $49.28 a share. Quoted in recent weeks at about $40 a share, Riggs traded in a range of $32.50 to $39.50 last year.