Louis Hagan Thorson and Richard Harrington Gregoryry III exchanged marriage vows last Saturday at Christ Episcopall Church here in Georgetown. The Rev. Sanford Garner Jr. performed the nuptial ceremony and also attended the reception held in the Bethesda, Md. home of the bride's parents, Phillip and Marit Thorson of Bethesda and Crystal Springs, Pa.

The bride graduated from Sidwell Friends School in this city and from Wells College (N.Y.). She is an assistant personnel officer with Development Alternatives, Inc., a Washington-based consulting firm. Her father is the former Director of Administration of the International Monetary Fund in Washington, D.C. and is now a consultant in international personnel management. Her mother is the Director of Volunteer Services of Montgomery County, Md.

Mr. Gregory, son of Richard H. Gregory Jr. of Bronxville, N.Y. and WESTERLY, R.I. and the late Mrs. Gregory, is a Phi Beta Kappa graduate of Amherst College with a law degree from the University of Southern California Law Center at Los Angeles where he was selected as a member of the Order of the Coif. He is now a trial attorney in the Tax Division of the U.S. Department of Justice. His father, now retired, was a member of the law department of the Union Carbide Corporation in New York City.

The couple will reside in Washington, D.C.