John Guinee Jr., long active in the Washington area real estate industry, yesterday was named president of Vienna-based Yeonas Co., one of Washington's largest residential building companies.

Guinee will succeed C. G. (Gus) Yeonas, who plans to concentrate on personal investments after he leaves a company founded by the Yeonas family 30 years ago. Yeonas was acquired by Oil-American Inc. in 1969.

A former vice president of administration for the Yeonas firm, which has built some 12,000 homes in the D.C. area, Guinee left Yeonas in 1968 to set up a small building company in Reston. Later he joined the Gulf Reston Inc. and became executive vice president of the Gulf Oil Corp. real estate operation.

Recently, Guinee was trustee and chief executive of the bankrupt Continental Mortgage Investors, now under jurisdiction of a federal court in Boston.

The 250 employes of Yeonas were informed of the executive changes yesterday afternoon. A statement by Olin President Benjamin Lake II said Gus Yeonas had been president since 1973. Lake said the Yeonas brothers would remain in a "counseling capacity during the change in management."

Gus Yeonas said the Olin sibsidiary that bears his family name "is stronger than ever before, thus making it timely for us to step down and devote our attention to personal interest." He is chairman of Providence Savings and Loan in Vienna.