Luciano Becchio's eight-yard strike, and neat finishes from Gradel and Howson propelled Leeds to victory.
Leeds took the lead when McCormack tapped into an empty net before Becchio's third from a tight angle.
The points were secured when Luciano Becchio played Howson through on goal and he coolly completed a maiden career treble.
But Max Gradel sparked a Leeds comeback when he angled in a shot before Luciano Becchio swept in an equaliser.
Leeds started to dominate and earned a deserved equaliser when Paul Connolly crossed for Becchio to score from close range.
Becchio stole in to add a third from a tight angle after Smith had failed to clear the danger in time added on.
Goals from Robert Snodgrass, Ross McCormack and Luciano Becchio saw Leeds defeat 10-man Ipswich and move to within a point of the play-off zone.
But Becchio's header found Gradel unmarked in the Burnley area and the winger produced an emphatic finish to pull one back for the visitors.
After Howson's rapid reply, the Leeds fans grew increasingly frustrated until Becchio put them ahead again with a close-range finish following a Leigh Bromby knock-down.
Jon Parkin gave Preston the lead from close range, before headers by Luciano Becchio and Alex Bruce and a double from Davide Somma put Leeds in control.
Leeds stormed back as Becchio nodded in George McCartney's cross to equalise and they were soon in front as Bruce took full advantage of Sean St Ledger's poor header.
But the final goal fell to the energetic Gradel, who fired home a rebound from six yards minutes before the end after Camp had denied substitute Jake Livermore and then Becchio.
Shortly afterwards, the Yorkshire side appeared to take a decisive grip on the contest when Becchio headed his 17th goal of the Championship season after Bromby's initial effort cannoned off the post.
And it was Leeds who pressed as Luciano Becchio's cross took an awkward bounce which Robert Snodgrass swung a leg at but the effort, just inside the area, went comfortably into the body of Randolph.
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