Detroit — Admittedly frustrated by their inability to increase shipments of subcompacts and compacts cars to the United States, the Japanese importers are focusing any styling changes for 1985-86 on sporty and midsize models, a move that is intensifying their competition with both the European imports and Detroit.
For 1985, the top-of-the-line Toyota Cressida and Nissan Maxima sedans are redesigned. Toyota will introduce a midship-engine, two-seater sports coupe called the SV, which will compete against the Pontiac Fiero and Mazda RX-7.
Nissan last spring introduced a revamped 200SX sports coupe line and, if 1985 -86 voluntary quotas are relaxed, will send the Micra minicompact to the US, along with the Prairie minivan.
The Prairie would contest in the growing minivan market against the popular Plymouth Voyager and Dodge Caravan, as well as the VW Vanagon, Toyota Van, Chevrolet Astro, and Ford Aerostar, due next spring.
Honda will go upscale in 1986 with the Executive midsize sedan, which will be imported from both Britain and Japan. Honda is co-developing the Executive, its first intermediate sedan, with Britain's BL PLC (formerly British Leyland). A two-seat sportster and possibly a minicompact called the City are also on Honda's future list.
Model-mix ''enrichment'' will bring a sporty coupe and a minicompact to Subaru this fall, while Mazda has added a diesel-engine option to its 626 compact. Isuzu has launched its Trooper II utility vehicle and will restyle its I-Mark sedans for 1985.
Mitsubishi's plans are linked to the projected Chrysler joint-production venture and a tie to Korea's Hyundai as a possible add-on. Mitsubishi now supplies all of Hyundai's engines.
Mitsubishi this year added a turbo for its Colt subcompact, imported by Chrysler, as well as to the Vista 7-seat wagon. A luxury Mitsubishi sedan, the Galant, and the subcompact Mirage have also been introduced.
Among the Europeans, VW is introducing its next-generation Rabbit, renamed the Golf, in keeping with its name in all other markets where it is sold. The imported Jetta also has been restyled for 1985.
Porsche, the exclusive builder of high-priced sports coupes, terminated a 15 -year VW-Audi connection Sept. 1 and become an independent importer. For 1985 Audi will offer additional 4-wheel-drive cars in the US, centered on the aerodynamic lines pioneered by the 5000S coupe two years ago.
The Mercedes-Benz plunge into the subcompact segment last fall with the 190 series will be followed by the 220, a slightly larger successor to the discontinued 240D sedan.
Volvo's top-of-the-line 760 sedan will get a 4-cylinder engine as the 740. Saab's 900 series will not be redesigned until 1986, but the coming model year will highlight a ''first'' from Sweden when a limited-edition convertible debuts.
From France, Peugeot has added a turbocharged diesel wagon to its 505 line sold in the US, while Renault has introduced the R-25 as its new flagship. The aerodynamic-looking R-25, plus a smaller version called the Laureate, are being mentioned for North American production by AMC in 1986.
Ford and West German automaker BMW have begun to offer American buyers a BMW turbodiesel engine in both the Lincoln and BMW 528e cars. The BMW engine is an option in 1985 on the Ford Thunderbird and Mercury Cougar as well.
Ford's status as the only domestic automaker not importing cars ended this fall when Lincoln-Mercury dealers put on sale the Merkur, a turbocharged V-6 coupe sold in Europe as the Sierra, to be followed up in 1986 by import of the Lugano from Ford of Europe, an upscale coupe for Ford dealers.
The sole imports from Britain and Italy, Jaguar and Alfa Romeo, will stand pat for early 1985. A redesigned Jaguar sedan is coming next year.
Alfa Romeo is looking at a new 4-wheel-drive system for adaptation to its sportsters sold in the US.