In a burst of promises as good as anything Detroit ever dreamed, the Soviet Union has unveiled the latest model of its luxury car "Seagull" - this one complete with air conditioning, radio and tape deck, automatic transmission and power steering and boasting a top speed of 110 m.p.h.

The official Soviet news agency Tass says production will begin this year on the model 14 "Seagull" ("Chaika" in Russian). "The new Chaika model answers all modern requirements," tass declared. "the new car is well-designed, dynamic and reaches 100 kilometers per hour in 15 seconds.

"It is very comfortable inside the car. The noise of the powerful engine does not annoy the passengers. There is an air-conditioning installation and built-in stereo car radio with a tape recorder. There is no clutch pedal - the auto has automatic gear box and power steering."

A photo of the new car in the journal "Trud" shows a low-slung body with the slightly boxy lines of the latest model Cadillacs, subdued chrome work and a tasteful grill. It is quite different in looks from the present Chaika, which according to a British car enthusiast now resident in Moscow "looks like nothing as much as a 1956 Mercury."

The car will have a 220-hp engine and will seat seven persons. It will be equipped with a bench-type rear seat, probably two bucket seats in front, and two fold down jump seats, an arrangement somewhat similar to the present Checker Cab.

Chaikas come in one known color - black. This is because they are reserved exclusively for Soviet officials. Ordinary citizens must stand in line for the much smaller cars that are the backbone of the Soviet Union's burgeoning auto industry - the Zhigulis, Moskvitches and Zaporozhets that crowd Moscow's increasingly congested streets.

Tass underscored the exclusively of the Chaika in its announcement. It did not quote a sticker price because there isn't any.

Besides, the total output would hardly keep a dealer awake. According to a senior editor at the Soviet auto magazine "Behind the Wheel," (monthly circulation 2.5 million, 80 kopecks a copy, subscription only) the Chaika plant presently is churning out its luxury vehicles at the rate of three every two days.