Mr. and Mrs. Robert Welch Mullen of New York City announce the engagement of their daughter, Mary Lou to Alexander Hamilton Spaulding, son of Mr. and Mrs. Josiah Augustus Spaulding of Manchester, Mass. A June wedding is planned.

Miss Mullen, an alumna of the Convent of the Sacred Heart in New York, expects to graduate this spring from Georgetown University. A provisional member of the Junior Leagua of New York, she was A provisional member of the Junior League of New York, she was presented at the League's 1975 Debutante Ball and at the Debutante Cotillion and Christmas Ball. Her father is a member of the New York law firm of Dickerson, Reilly & Mullen.

She is the granddaughter of Raymond H. Reiss of New York and Deal, N.J., the industrialist and former Chairman of the Board of Trustees of Georgetown University, and the late Mrs. Reiss; and of the late Arthur Clarnce Mullen, a New Jersey attorney and a member of the firm of Armstrong & Mullen, and the late Mrs. Mullen. She is the great-granddaughter of the late J.L. Reiss, the philanthropist.

Mr. Spaulding is an alumnus of the Groton School, graduated from Concord Academy and attended Bowdoin College. He is a senior at Georgetown University and intends to enter law school this fall. He is the grandson of the late Mr. and Mrs. Paul W. Spaulding of Worcester, Mass., and of the late George Temple Bowdoin of Oyster Bay and New York, a founding partner of Morgan and Company. He is a direct descendant of Alexander Hamilton, the first Secretary of the Treasury, and of James Bowdoin, the first Governor of Massachusetts and founder of Bowdoin College. Mr. Spaulding's step-grandfather, Edward H. Foley, was the Undersecretary of the Treasury in the Truman Administration and his maternal grandmother is Mrs. Edward H. Foley of Washington, D.C. The prospective bridegroom's father is an attorney in Boston and was a Republican candidate for the U.S. Senate from Massachusetts in 1970 and the Republican candidate for Attorney General of the Commonwealth in 1974. His mother is on the executive committee on the Board of Trustees of Boston University and active in Massachusetts charities.