‘Rule’ of thumb: Use De Niro as topliner

Bowman being considered as helmer

Robert De Niro will topline Fox 2000 actioner “Rule Number Three.” Studio is circling director Rob Bowman, the TV helmer-turned-feature director who has directed “The X-Files” and “Reign of Fire.”

Robert Kuhn-scripted project, which mixes drama and comedy, has long been considered a strong star vehicle. Story concerns an arrogant firearms tycoon who attempts to bully a seemingly average guy; latter turns out to be an accomplished assassin who decides to give the gun guy a serious lesson in humility.

Lawrence Grey and Gil Netter are producing “Rule Number Three,” which is likely to shoot next year. The Zucker-Netter Prods. banner originally set the project at Fox 2000.

De Niro’s about to return as the angst-ridden hit man alongside shrink Billy Crystal in “Analyze That,” and he’s also expected to turn in a sequel performance in “Meet the Fockers,” the second installment of “Meet the Parents” at Universal. Thesp goes back into serious mode when he directs and co-stars with Leonardo DiCaprio in U’s CIA drama “The Good Shepherd.” De Niro is repped by CAA.