Forster, who started his career at Gillingham, wasted a great chance to score on his return, and was a constant threat, up against Gillingham defenders Chris Hope and Barry Ashby.
Ashby cleared the ball off the line early in the second half after Forster had got to the by-line, before cutting the ball back and earlier David Perpetuini also did the same just before half time when goalkeeper Jason Brown charged off his line but missed his punch.
Gillingham paraded Marlon King for his first start since being released from prison but Paul Shaw cried off with a stomach bug which also affected player-manager Andy Hessenthaler and skipper Paul Smith.
King shot wide early on before Hope was denied by a good punch clear by Reading keeper Marcus Hahnemann who had an impressive afternoon between the sticks for the Royals.
Reading had to make a change just after the hour-mark when Matthew Upson was forced off with a cut eye after clashing heads with Gillingham's big striker Mama Sidibe. Upson needed eight stitches in the wound.
Reading looked dangerous on the break the longer the game went on and James Harper flashed another effort just past the far post.
Winning boss Pardew said: " We showed the character and resilience to deal with Gillingham's threat and aggression."
The defeat was Gillingham's second in a row at home and they looked jaded towards the end following their midweek Worthington Cup defeat at Chelsea.
However coach Wayne Jones was not using that as an excuse saying: We didn't play very well but without sounding negative or pessimistic, I think we hoped to get a point before they scored.".