DETROIT — The Republican tax proposal has clouded the outlook for electric vehicles in the United States.

The congressional plan presented on Thursday, which would abolish a $7,500 federal income-tax credit for electric vehicles, arrives just as automakers are gearing up to expand their lineups.

The credit for purchases of all-electric and plug-in hybrid cars has been a key incentive for consumers to consider switching from traditional gasoline-powered models.

The credit has also helped automakers stimulate the market for electrified models, as well as cover their costs as they build a customer base.