Loretta Tofani, of the metropolitan news staff of The Washington Post, won the Grand Award in the annual Front Page Awards competition sponsored by the Washington-Baltimore Newspaper Guild.

Tofani, 30, was honored for her series titled "Rape in the County Jail" that detailed a pattern of sexual assaults in the Prince George's County Detention Center. She has won several other awards for the series, including a Pulitzer Prize

Tofani also won the Guild's Public Service award for her series. The Frank C. Porter Memorial Award for Labor Reporting went to Karlyn Barker of The Post. Another metro staff reporter, Chip Brown, won the award for features.

In photography, Doug Chevalier of The Post was selected winner of the Grand Award for his photo titled "Aftermath of Airline Disaster," which also won the Guild's prize for local news photography.

In addition to the Grand Award for writing, staff writers for The Post won five of the eight Front Page Awards given for newspapers of general circulation. The other three awards went to staff members of the Baltimore Sunpapers. The three eligible newspapers--The Post, The Baltimore Sun and The Evening Sun--submitted a total of 127 entries.

In addition to the Grand Award in photography, photographers for The Post won awards in three of the seven other categories considered by the judges.

Staff members of The Post and the Sunpapers submitted 106 entries.

In addition to those already mentioned, Post winners in the writing categories were: Local News--Athelia Knight and Benjamin Weiser for their series "Street Cops," and National News--Victor Cohn, Philip J. Hilts and Cristine Russell for their series "Brain Waves."

Barker won her labor award for a series titled "The Job Hunt," and Brown won his feature award for a series titled "A Question of Will."

Other photography categories in which Post staff members won awards are: Features--Gerald Martineau, for "Walkman-Balloonman," and Sports--Gary A. Cameron, for "Snow Sack."

Miriam Grant of The Washington Post won a First Award in the category of Advertising Promotion.

The Washington-Baltimore Newspaper Guild is a labor union that represents editorial and commercial employes on The Post and The Sunpapers, and also represents employes of several other enterprises. Judging was held Tuesday. Entries were for work performed in 1982.