This is not just a generic reference to the Porky Pig character; Pynchon is referring to a specific cartoon, 'The Blow-Out' (1936). It was directed by Tex Avery and animated by Sid Sutherland and Chuck Jones. At this point, Porky Pig was still voiced by Joe Dougherty, before Mel Blanc took over the role in the late 1930s.
In 'The Blow Out', a young Porky Pig is doing favours for people to raise money for ice-cream. He crosses paths with the Mad Bomber character and, thinking he has dropped his bomb by accident, keeps returning it to him until the inevitable explosion.
Pynchon also referenced this particular cartoon in The Crying of Lot 49. The image of Porky Pig returning the bomb is mentioned later in Gravity's Rainbow as part of a hallucinatory montage.