Morton Mintz of The Washington Post won the grand award in the reporting category in the Washington-Baltimore Newspaper Guild's Front Page Awards contest, it was announced yesterday.

Mintz won the award for his five-part series on the Dalkon Shield contraceptive device and the problems caused by its use. Mintz's series also won first place in the public service category.

Peter Perl of The Post won the Frank Porter Memorial Award for Labor and Business Reporting with an article on what workers are not told by employers about possible exposure to potential health risks on the job.

John Mintz of The Post won first place in the investigative reporting category for a series on political figure Lyndon H. LaRouche Jr., and Don Oberdorfer won first place in the national news category for articles about the Reagan administration's interpretation of the ABM treaty.

Ed Bruske of The Post was a first-place winner in the local news reporting category for an article about an 11-year-old who was assaulted while in court custody. Ken Denlinger of The Post won first place in sports writing and Dennis McAuliffe, a Post copy editor, won a first-place award for headline writing.

Dudley M. Brooks of The Post was the grand award winner in photography for pictures taken after last year's Mexican earthquake. The pictures also won first place in the picture story category.

In other photography awards, Larry Morris of The Post won first place in the local news category, Frank Johnston of The Post won first place in the portrait category, Gary Cameron of The Post won first place in the sports category and Gerald Martineau of The Post won a first-place award in the national news category.

The winners of the 1985 Sigma Delta Chi distinguished service awards, which also were announced yesterday:

General Reporting (circulation of less than 100,000): Art Geiselman, Albuquerque (N.M.) Journal.

Washington Correspondence: James O'Shea and Nicholas M. Horrock, Chicago Tribune.

Foreign Correspondence: Robert J. Rosenthal, The Philadelphia Inquirer.

News Photography: Jay Dickman, Dallas Times Herald.

Editorial Cartooning: Doug Marlette, The Charlotte (N.C.) Observer.

Public Service in Newspaper Journalism (circulation of more than 100,000): Detroit Free Press.

Public Service in Newspaper Journalism (circulation of less than 100,000): The Arizona Daily Star

Magazine Reporting: Mark Singer, The New Yorker.

Public Service in Magazine Journalism: Tropic, the Sunday magazine of The Miami Herald.

Radio Reporting: Tony Hanson, Richard Maloney and Larry Litwin, KYW-AM, Philadelphia.

Public Service in Radio Journalism: KGO-AM in San Francisco.

Editorializing on Radio: Nicholas DeLuca and Joan Margalith, KCBS-AM in San Francisco.

Television Reporting: WFAA-TV in Dallas.

Public Service in Television Journalism (stations in the top 50 markets): KPRC-TV in Houston; (stations in all other markets): KTUL-TV in Tulsa.

Editorializing on Television: Phil Johnson, WWL-TV in New Orleans.

Research About Journalism: Prof. Leonard W. Levy, Claremont College in California.