Most of what comes over the Salvadoran guerrilla movement's Radio Venceremos is grim, a diet of battle reports and political attacks that start with the sound of machine-gun fire and end with revolutionary slogans. There was a welcome change a few days ago, however, and the cause was U.S. Ambassador Deane R. Hinton.

The envoy, in addition to being a veteran diplomat, is a widower. His plans to marry a Salvadoran woman on Valentine's Day inspired some unusual guerrilla wit for a special addition to the broadcast.

The rebel radio titled its report "Love Story." Tongue in revolutionary cheek, it suggested the marriage was cooked up not in heaven but in the salons of El Salvador's wealthy, where it said patrician ladies designated the bride as a sort of rightist mole to influence the diplomat.

" 'Let's give him to Patty,' said Dona Florita," went the radio's imaginary conversation. " 'Patty Hearst?' asked Dona Marillita. 'No no, she is very young and will finish the old boy off. I mean Patty Salaverria,' explained Dona Florita."

Hinton "fell into the trap," the radio said, and so will be getting married with "the flower of the oligarchy, although a little faded, Dona Patricia Salaverria."

"We already imagine Mister Hinton answering his adorable Juliet," the broadcast continued. " 'Listen, Hin, we need military aid.' 'Yes, my love.' 'Listen Hin, the State Department should change its policies toward our country.' 'Yes my love.' 'They should abandon the "fish" slang term for the Christian Democrats, considered too moderate by the far right .' 'Yes, my love.'

"In conclusion, that which the oligarchy could not win in the diplomatic struggle, it has won in the wedding bed. Congratulations, Mister Hinton."