HOBOKEN, N.J. (AP) _ Maxwell House will close its 50-year-old coffee roasting and grinding plant here by early 1992 and expand a plant in Jacksonville, Fla., the company announced Wednesday.

None of the 600 workers at the Hoboken plant would be laid off immediately, said Raymond G. Viault, company president.

''People simply aren't drinking as much coffee as they used to,'' Viault said.

A 24 percent decline in American coffee consumption since 1963 left Maxwell House's four United States plants operating at only 55 percent capacity, Viault said at a press conference in Secaucus. In February, parent company General Foods USA announced that either Hoboken or Jacksonville would be closed.

Despite workers' concessions and enticements from the city, the company chose the 66-year-old Jacksonville site, where workers make an average of $3 an hour less.

As positions are phased out, workers would be offered counseling, retraining and possible relocation to other positions in General Foods and its parent company Philip Morris Co., Viault said.

Jacksonville operations manager Frank Meegan said that over the next 18 months, new roasters and process control equipment would be installed and production would be expanded by 40 percent.

The plant's 380 workers cheered the news when it was announced Wednesday afternoon.