Energy tax seminar presented by the National Coal Association and the International Petroleum Association of America begins today with an overview of tax reform at 1:30 p.m. and a discussion of the mechanics of energy tax provisions at 2:30 p.m., both in Room SD-G-50, Dirksen Senate Office Building; and continuing at 5 p.m. with a congressional reception, in SD-562, Dirksen. Call John Grasser at 463-2651 for information. TUESDAY

General Assembly of the International Scientific Committee on Problems of the Environment meets through Friday, Auditorium, National Academy of Sciences, 2100 C St. NW. Environmental experts from the People's Republic of China, Brazil, France, Venezuela and the United States will speak. Free. Call Ruth DeFries at 334-3060 for information. Javier Perez de Cuellar, secretary general of the United Nations, speaks to the National Press Club. A luncheon at 12:30 p.m. will be followed by the speech at 1 p.m., 14th and F streets NW. Cost is $16 for lunch. Call Juan Carlos Brandt at 289-8670 for information. WEDNESDAY

Health fraud is the topic of a conference that features representatives from over 100 national organizations, beginning with coffee and registration at 7:30 a.m., Ballroom, National Press Club, 14th and F streets NW. Cost is $25. It is sponsored by the Food and Drug Administration, the Federal Trade Commission and the U.S. Postal Service. Call 443-5006 for information. Carl Sagan lectures on nuclear winter, 7:30 p.m., Gilbert H. Grosvenor Auditorium, National Geographic Society, 1600 M St. NW. The lecture is sponsored by the Audubon Naturalist Society and the Smithsonian Resident Associate Program. Tickets are $5 for members of sponsoring organizations, $7 for nonmembers. Call 357-3030 for information. THURSDAY

"International Terrorism -- Response and Reaction" breakfast briefing featuring Moorhead Kennedy and Robert Kupperman, 8 a.m., West Ballroom, Sheraton Grand Hotel, 525 New Jersey Ave. NW. Kennedy, a former Foreign Service officer who was held hostage in Iran, is executive director of the Council for International Understanding. Kupperman is a senior associate at the Georgetown Center for Strategic and International Studies. Call 393-0772 for reservations and information. Association of Political Risk Analysts' conference entitled "The United States as a Political Risk: Boom or Bust for Business?" begins with a cocktail reception at 6 p.m., Faculty Lounge, Intercultural Center, Georgetown University; and continues Friday with registration beginning at 8:30 a.m., Hall of Nations, Walsh Building, 36th Street NW. Speakers Friday include Roman Senkiw, president of APRA; Gordon Rayfield, a political analyst with General Motors Corp., and William Colby, former director of the Central Intelligence Agency, who will moderate a panel discussion. Registration is $190 for members, $290 for nonmembers. Call 293-5913 for information. FRIDAY

Society for History in the Federal Government sponsors a program entitled "Federal Information Management: Setting the Agenda," beginning with registration at 8:30 a.m. and continuing with sessions featuring representatives from the Center of Military History, the State Department, the National Institutes of Health and the Federal Bureau of Investigation, Coolidge Auditorium, Library of Congress. Cost is $10. The symposium will explore issues related to the availability of government information. Call Ken Thibodeau at 496-2832 for information. President's Commission on Americans Outdoors meets at 9 a.m., Room 2856, National Geographic Society, 1146 16th St. NW. This is an organizational meeting. Call 343-4905 for information.