Joan G. Day and Carter insider Vicki Bagley have ended their year-old cooperative real estate venture, called Joan G. Day, Ltd.-Vicki Bagley Realty, Inc. Day and Bagley will operate separate firms in Georgetown and continue to hold joint interests in the Middleburg realty office of Boteler, Bagley & Day.

Lew Sichelman, real estate editor of the Washington Star, will be the moderator of a Wednesday morning workshop of the sales and marketing council of the Suburban Maryland Home Builders Association at the Ramada Inn in Lanham.

James H. McMullin, who heads Real Estate Service, Inc., in Arlington, has been elected president of the George Washington chapter of Lambda Alpha, an international land economics fraternity. Other officers are Herbert Franklin, Donald Priest and Julie Levine.

Jerry Smith, recently retired tight end of the Washington Redskins, has announced that his home building firm, Smith Bros., Builders, Inc., has broken ground for a new community of 176 single-family houses on Edward Ferry Road in Leesburg. The traditional models will be shown in April. Prices will begin in the $60,000 range.

Milton H. Miller has been named president of the Washington office of Kornblatt Associates. While directing the Washington office, Miller will continue as corporate vice president of the firm in Baltimore.

Arthur Sutherland has been named branch manager of the new office of the John Hanson Service Corp. in Northern Virginia.

Gene Kijowski will conduct a workshop on swimming pools Tuesday evening at the Key Bridge Marriott, where the area chapter of the Community Associations Institute will meet.

Broker George G. Rink has been named sales manager for the Reston office of Jerry Sardone Realty, Inc. Rink, who has been a million-dollar sales agent with the firm, also serves as chairman of the grievances and ethics committee of the Northern Virginia Board of Realtors.