Memorial Day is observed. TUESDAY

Presidenagan announces his tax-simplification plan in a nationally televised address at 8 p.m. Assistant Secretary of State Richard R. Burt speaks on "U.S.-Soviet Relations and Arms Control" before the World Affairs Council of Washington at noon at the Capital Hilton Hotel. For more information, phone 293-1051. WEDNESDAY

The president addresses a White House sponsored coalition on tax simplification and meets with Jordan's King Hussein. The National Governors' Association holds a three-day conference in Des Moines to study the long-term impact of the farm crisis. For information on the event, "Agriculture in Transition: Impact upon the Family, the Community and the Economy," phone 624-7734. Cardinal Jaime Sin of the Philippines addresses a 12:30 p.m. luncheon at the National Press Club. The National Commission Against Drunk Driving holds a 10 a.m. news conference at the Mayflower Hotel on its nationwide inventory of legislation and programs related to drunk-driving issues. THURSDAY

Reagan delivers speeches in Williamsburg and Oshkosh, Wis. A group representing 53 Nobel laureates and more than 700 members of the National Academy of Sciences holds a news conference to appeal for U.S.-Soviet agreement to ban space weapons. It will be held at 9:30 a.m. at the National Press Club. The National Association of Personal Financial Advisers holds a 12:30 p.m. briefing at the press club on the implications of the president's tax-simplification plan on the personal investor. FRIDAY

The president makes an appearance at Great Valley Corporate Center in Malvern, Pa.