DETROIT (AP) _ General Motors Corp.'s 70-year-old Fleetwood Cadillac plant built its last Brougham body on Wednesday, and a partner plant that mates the Fleetwood bodies to chassis will shut Friday.

About 1,500 workers at the southwest Detroit factories lost their jobs Wednesday and another 1,500 at its Clark Street partner will be laid off Friday. In June, 3,000 Fleetwood workers were laid off.

GM had built a replacement front-wheel-drive Cadillac plant in the Detroit enclave of Hamtramck, but kept the outmoded Fleetwood and Clark Street plants open because of the surprising staying power of the rear-wheel-dri ve Fleetwood.

The Fleetwood now will be built at a GM plant in Arlington, Texas. The Arlington plant also will build two other venerable rear-wheel-drive models, the Chevrolet Caprice and Oldsmobile Custom Cruiser station wagon.

As at other GM assembly plants that have closed, including the Flint Body and Pontiac Assembly partners closed last week, one Fleetwood worker and one Clark Street worker won the last two Broughams in a drawing.

The winners may be among a few GM workers to disprove the first few lines of the 1985 song ''C-I-T-Y'' by John Cafferty and the Beaver Brown Band, one of several that have mentioned the famous plant:

''On the south side of Detroit City I'm working all night on the line. Under black smoke stacks building Cadillac, Jack. Not one of them will ever be mine.''

Fleetwood and Clark were once thought to be among GM's most secure plants because they built Cadillacs, the premier status car in the United States until the 1970s.

The plant began as a World War I government war plane factory. In 1919, it was bought by the Fisher brothers, who built auto bodies and who built the main six-story building in 1922.

Fisher Brothers, which became a GM division in 1926, bought Fleetwood Custom Body Co. of Fleetwood, Pa., in 1925 and moved the operation to the Detroit plant, which they renamed Fleetwood.

Fleetwood built all Cadillac bodies until the late 1960s, as well as bodies for LaSalle from 1926 to 1940. In the past few years, the paired plants also made the Caprice and Custom Cruiser which since have been moved to Texas.

Officials at United Auto Workers union Local 15, which represents Fleetwood, have held rallies, written letters and distributed pamphlets for the last year calling for legislation to halt plant closings.

They are particularly worried because the two plants that will do their plant's work - Arlington and Hamtramck - cannot take worker transfers since both have a shift of workers on layoff and are working only one shift.

One of the union's rallies took place late Wednesday morning, in front of the plant, said Local 15 official Danny Moore. ''Everyone will be unemployed. There's no protection because we have no job to go to,'' Moore said.