Lionel H. Olmer, undersecretary of Commerce for international trade and head of the International Trade Administration, will join the law firm of Paul, Weiss, Rifkind, Wharton & Garrison as a partner in its Washington office, effective June 17, the New York-based law firm announced Thursday.

Olmer, who has been in the administration's trade hot seat since 1981 trying to win broader American access to foreign markets, soon will be representing the firm's growing number of U.S. and foreign clients on matters of international trade and investment. Those clients include Mitsubishi Corp., Revlon Inc. and Aetna Life & Casualty Co.

Olmer joins a host of other notable ex-government officials at the law firm, including Morris B. Abram, vice chairman of the U.S. Commission on Civil Rights; Theodore C. Sorensen, special counsel to presidents Kennedy and Johnson; Matthew Nimetz, State Department counselor under President Carter, and former Internal Revenue Service commissioner Jerome Kurtz.

A graduate of American University's law school and a member of the D.C. and Connecticut bars, Olmer joins private law practice after many years in government and private industry. From 1977 until his trade appointment, he was director of international programs for Motorola Inc. Before that he served for nearly five years on the President's Foreign Intelligence Advisory Board, ultimately as staff director. In the 1960s, Olmer was an officer in the U.S. Navy, including an assignment with the staff of the Chief of Naval Operations.

Olmer's plans to leave his job at Commerce have been known for several months, as has the name of his successor, S. Bruce Smart Jr. Smart left his job as chairman and chief executive officer of Continental Group Inc. in February after a merger. COMMUNICATIONS

Michael A. Brunner, vice president for government communications at AT&T Communications, has been named executive vice president for the federal systems division, replacing Robert E. Gradle, who has retired. A 30-year veteran of AT&T, Brunner will oversee all AT&T Technology Systems' marketing to the federal government.

Western Union Telegraph Co. has appointed Larry E. Willner vice president and general manager of its government systems division. Willner joined the division, which provides telecommunications systems to the federal government, after a 26-year career in the U.S. Army.

Gary Auxier, press secretary for former Sen. Walter D. Huddleston (D-Ken.), has joined the public relations firm of Burson-Marsteller as a senior account executive. Previously, Auxier was director of communications for the Senate Small Business Committee and a press secretary for former Kentucky Gov. Julian M. Carroll.

Cellular One, one of two mobile phone services licensed to operate in the Washington area, has tapped two out-of-towners to help manage operations: Charles K. Mills, formerly with GTE Mobilenet in Michigan and Ohio, has been named cellular systems supervisor. Roger W. Beckman, recently with Archer Services Inc. in Los Angeles, has been named customer service manager.

NC Broadcast News, a division of the National Catholic News Service, has appointed Hal Levenson senior producer of NEWSFRONT, a nationally televised newscast covering religious events and issues. Levenson has held news management positions with Metromedia Inc.'s Washington and New York stations and recently produced and wrote the documentary "Nuclear Power and the Press" for the public television series "Inside Story." RETAIL, WHOLESALE TRADE

Pete L. Manos, head of Giant Food's perishable food operations since 1983, has been given the additional title of senior vice president for food operations -- a new position at the supermarket chain. Gerson Barnett, formerly senior vice president for grocery operations, has retired. No replacement for Barnett will be named, a company spokesman said. Also, Phil Montgomery, formerly manager of the Giant store on Old Georgetown Road in Bethesda, has been named manager of Giant's new Herndon store. INDUSTRIAL, MANUFACTURING

Harnischfeger Corp., the Milwaukee-based equipment manufacturer, has named Joseph A. Devlin vice president for government affairs in its new Washington office. Also, Judy Moran was appointed manager of government marketing and Ed Tokarz was named supervisor of government sales.

James C. Fletcher, formerly administrator of the National Aeronautics and Space Administration and a former president of the University of Utah, has been elected a director of Fairchild Industries Inc., the Chantilly-based aerospace and electronics conglomerate. GOVERNMENT

After a brief stint in the private sector, Walter A. Varvel has returned to the Federal Reserve Bank of Richmond as vice president, effective June 10. He joined the bank in 1974 as an economist and was named an assistant vice president in 1983. Last year he left the bank to join a private business in Texas.

Virginia's Department of Industrial Development has named Mark R. Kilduff deputy director for industrial development, replacing Hugh D. Keogh, who has left the government. Kilduff has been with the industrial development program since 1967, most recently as director of marketing and chief economist.

The U.S. Government Printing Office has named James D. Young director of documents sales service and Charles B. McKeown director of marketing. Young, who joined GPO in 1970, was assistant to the director of document sales service. McKeown, who has 25 years of marketing experience, cofounded The Adams Group Inc., an advertising and public relations firm, in 1968. Most recently, he was the GPO's deputy director of marketing.

W. Churchill Robison, formerly on the congressional relations staff of the International Trade Administration, has joined the Washington office of the Port Authority of New York and New Jersey. BANKING AND FINANCIAL SERVICES

Shareholders of the Federal National Mortgage Association recently elected Roger E. Birk, chairman emeritus of Merrill Lynch & Co. Inc., and James A. Aliber, chairman and chief executive officer of First Federal of Michigan, to its board of directors.

Louis G. Fields Jr., U.S. representative to the Conference on Disarmament for the past four years, has rejoined the board of directors of First Commercial Bank in Arlington. Fields, one of the bank's original directors, became a partner in the Washington law firm of Vance, Joyce, Carbaugh, Huang, Field and Crommelin in January.

Charles L. Dempsey, formerly inspector general of the Department of Housing and Urban Development, has joined Alexander Grant & Co., an accounting firm, as director of government services.

Riggs National Bank has appointed Edward P. Alton, formerly a vice president of Equibank in Pittsburgh, to the post of regional vice president in the retail banking group.

At their recent annual meeting, stockholders of Second National Building & Loan, Maryland's only publicly owned S&L, elected Harry Bonk, chairman and chief executive officer of Draper-King Cole Inc., a Delaware-based cannery and agricultural firm, and William E. Knight, senior partner in the Prince George's County law firm of Knight, Manzi, Brennan & Ostrom, to its board of directors.

George L. Nolin, president of the real estate firm George L. Nolin & Associates Inc., and James L. Eichberg, president and director of Smithy Braedon Co., have been elected directors of National Bank of Commerce.