General Motors Co
GM also said that its production of Volt and Ampera will be 16,000 in 2011, up from a previous forecast of 15,000.
The plant in Detroit that makes the two plug-in hybrids will shut for four weeks starting in early June, which will crimp already tight supplies, GM said.
Volt, the poster car for GM's effort to tilt its model lineup toward fuel-efficiency from gas-guzzling, will experience delays in dealer deliveries this summer as gasoline prices could soar over $4 per gallon, GM said.
Already in tight supply, the number of Volts available for delivery to retail customers will be further restricted over the next three months before production resumes and the Volt and the Opel Ampera begin being exported to Europe and China, GM said in a statement.
Volt sales are to be especially reduced in June and July, GM said.
In April, Volt U.S. sales were 493, and for the first fourth months sales of this year sales are 1,703. It debuted late last year.
The Detroit-Hamtramck plant's shutdown will allow for retooling and other changes on the single assembly line for the new 2012 model year for the Volt and Ampera, said Rob Peterson, GM spokesman.
Of the 60,000 Volt and Ampera to be produced in 2012, 45,000 will be delivered in the United States and the remainder mainly in Europe, but also in Canada and China, GM said.
A first-of-its kind car, the Volt gets 379 miles on a full charge and full fuel tank, based on EPA estimates, but that driving range depends on driving habits.
For the first 35 miles or so, the car runs fully on electric power stored in a 16-kilowatt-hour lithium-ion battery.
A gasoline-powered 1.4-liter engine extends its range to the estimated 379 miles.
Cristi Landy, director of Volt marketing, said the car will be sold throughout the United States by the end of this year, and that the increased production is a result of high demand.
The Volt has been sold so far in California, New York, Connecticut, Maryland, Michigan, New Jersey, Texas, Virginia and Washington, D.C.
The Volt costs $41,000 including delivery costs before a $7,500 federal tax credit.
The Detroit-Hamtramck plant currently also makes two sedans, the Buick Lucerne and the Cadillac DTS, that the automaker is phasing out. They will no longer be made when the Detroit-Hamtramck plant reopens in July, Peterson said.
The plant shuts for the first two weeks of July annually and this year's shutdown is extended by two weeks to allow for the changes to the plant, GM said.
GM also said that the 2013 Chevrolet Malibu sedan Eco model, which GM says will get 38 miles per gallon in highway driving, will also be made at the Detroit-Hamtramck plant starting in 2012.
The Malibu Eco model will have E-Assist, which is an electric motor that boosts power to the engine during stops from a standing start and also when accelerating on freeways, which will save gasoline, GM says.
(Reporting by Bernie Woodall, editing by Bernard Orr)