Among the largest lecture bureaus in the country, according to the American Platform Association:

Conference Speakers International*, Suite 300, 1055 Thomas Jefferson St., Washington, D.C. 20007. Phone: 202-833-2344. Janet LeBrun Cosby, president. Commission: 15 to 25 percent of lecture fee. Clients: Eric Sevareid, Clare Boothe Luce, Kurt Vonnegut and Arkady Shevchenko.

Keppler Associates, Inc.*, Suite 400, 1825 I St. NW, Washington, D.C. 20006. Phone: 202-429-2030. James Keppler, president. Commission: 15 to 30 percent of lecture fee. Clients: former prime minister Harold Wilson, William F. Buckley Jr., Sam Donaldson and Gov. Jerry Brown.

Washington Speakers Bureau*, No. 11, 201 N. Fairfax St., Alexandria, Va. 22314. Phone: 703-684-0555. Harry Rhoads Jr., president. Commission: 20 percent of lecture fee. Clients: Lyn Nofziger, James J. Kilpatrick and Howard K. Smith, Chris Wallace and Steve Bell.

American Program Bureau, 850 Boylston St., Chestnut Hill, Mass. 02167. Phone: 617-731-0500. Ken Eisenstein, president. Commission: 10 to 30 percent of speaker's fee. Clients: Ralph Nader, Jack Anderson, Julian Bond, Bill Monroe and Gen. David Jones.

Harry Walker, Inc., Suite 3616, 350 Fifth Ave., New York 10118. Phone: 212-563-0700. Don Walker, president. Commission varies with each speaker. Clients: Henry Kissinger, Gerald Ford, Helmut Schmidt, Kurt Waldheim and Walter Mondale.

Lordly and Dame, Inc., 51 Church St., Boston 02116. Phone: 617-482-3593. Samuel Dame, president. Commission: 5 to 30 percent of speaker's fee. Clients: F. Lee Bailey, Dr. Joyce Brothers, Maya Angelou and George Plimpton.

Potomac Speakers, Inc., 3001 Veazey Ter. NW, Washington, D.C. 20008. Phone: 202-362-0005. Judith Geller, director. Commission: 20 to 30 percent of speaker's fee. Clients: Cyd Charisse, Jane Russell, Victor Borge, Larry King (talk show host) and Joan Mondale.

Richard Fulton, Inc., Suite 11C, 101 W. 57th St., New York 10019. Phone: 212-582-4099. Richard Fulton, president. Commission: 33 percent of speaker's fee. Clients: Edwin Newman, Gary Collins, Billy Martin, Frank Cappiello and Bess Myerson.

Royce Carlton, Inc., 866 United Nations Plaza, New York 10017. Phone: 212-355-3210. Carlton Sedgeley, president. Commission: 35 percent of speaker's fee. Clients: Dick Cavett, Vincent Price, Douglas Fairbanks Jr., Carl Bernstein and Simon Wiesenthal.

The Wagner and Baroody Group, 1100 17th St. NW, Washington, D.C. 20036. Phone: 202-466-8225. Joe Baroody, president. Commission: 15 percent of speaker's fee. Clients: Mideast expert Judith Kipper, former assistant secretary of state Harold Saunders and anchorman Bryant Gumbel.

* Indicates one of the top three fastest growing lecture bureaus in the country, according to Daniel Moore Jr., president of the American Platform Association.