*Economists representing the Heritage Foundation, Brookings Institution, Cato Institute and the American Enterprise Institute issue a statement on "the perils of trade protectionism," 11 a.m. at the foundation's Davis Policy Center, 214 Massachusetts Ave. NE.

*The reuse of disposable medical devices is the topic of a two-day conference sponsored by Georgetown University's Institute for Health Policy Analysis, and the Georgetown Law Center, beginning today at the Mayflower Hotel. Phone 783-8440 for details.

*Transportation Secretary Elizabeth Hanford Dole addresses a conference on alcohol and drug use in the railroad industry at 9 a.m. in the Federal Aviation Administration auditorium, 800 Independence Ave. SW.

*Sen. David F. Durenberger (R-Minn.) discusses problems raised by counterterrorist activities, and the implications for congressional oversight, at 7 p.m. at the Johns Hopkins University School for Advanced International Studies, 1740 Massachusetts Ave. NW. TUESDAY

Defense Secretary Caspar W. Weinberger is the luncheon speaker at a conference on arms control and the Strategic Defense Initiative. The event will begin with registration at 8 a.m. in the Federal Room of the Capital Hilton. Phone 682-1200.

*Foreign investment in the Third World is the topic of an Overseas Development Council conference at the Sheraton Carlton Hotel.

*The World Reources Institute holds a news conference on solutions for tropical deforestation, beginning at 9:30 a.m. at 1735 New York Ave. NW. Phone 638-6300. WEDNESDAY

* President Reagan travels to New York to mark the 40th anniversary of the United Nations.

*The Bureau of Labor Statistics issues releases on September consumer prices and real earnings.

*The Institute for Research on the Economics of Taxation sponsors a seminar on tax reform at the Madison Hotel. THURSDAY

Reagan addresses the United Nations General Assembly and meets with leaders from Britain, Canada, Italy, Japan and West Germany to review allied positions before the coming summit meeting.

*National Oceanic and Atmospheric Administration specialists meet with representatives of the commercial fishing industry to discuss NOAA's fisheries information services, 1 p.m. in Room 4830 of the Hoover Building, 14th Street at Constitution Ave. NW. The Committee on the Present Danger releases the results of a poll on public attitudes on the Strategic Defense Initiative at a 10:30 a.m. press conference at the Jefferson Hotel.

*"Family and Educational Excellence" is a seminar on issues for policymakers, and features Mary Hatwood Futrell of the National Education Association and William Kristol, special assistant to the secretary of education. Sponsored by the George Washington University School of Education and Human Development and the Home and School Institute, it begins at 9 a.m. at GW's Marvin Center. Phone 676-6160.

*The Cato Institute presents a policy forum on "The United Nation's War on Economic Freedom," at 4 p.m. at the institute, 224 Second St. SE. Phone 546-0200.

*The Association for Public Policy Analysis and Management sponsors a three-day research conference, starting today at the Shoreham Hotel. Phone (919) 684-6612. FRIDAY

The American College of Utilization Review Physicians sponsors a three-day seminar on "Health Care -- The Impact of Government and Corporate America," beginning today at the J.W. Marriott Hotel.