** Shares of truck maker Paccar PCAR.O fall 5.9% to $96.31 premarket

** The U.S. Environmental Protection Agency said on Wednesday it is starting efforts to reverse the Biden administration's vehicle emissions rules that would force automakers to build a rising number of electric vehicles

** Analysts have said trucking fleet firms had been expected to "pre-buy" trucks before the rules took effect, driving up demand, but this is now unlikely to happen

** Truck engine maker Cummins'CMI.N shares fall 2.9% to $321.05

** Shares of European truck makers also fell on Thursday

** PCAR stock down 10.8%, while Cummins is up 22.59% in the past 12 months

(Reporting by Padmanabhan Ananthan)

((Padmanabhan.Ananthan@thomsonreuters.com;))