VOLVO HAS DISCOVERED that there's sex after marriage, passion persisting between people with children. Why else would the Swedish automaker design something as fine and sleek as the 740 Turbo station wagon for 1986?

And sleek is only half of it. This wagon moves.

The 740 Turbo feels like a sports car. It zooms in and out of traffic with such agility as to make you forget that it also was built to haul kids, dogs and groceries.

Volvo is loosening up a bit, which is not to say that it's abandoning its traditional virtues of durability, reliability and safety. Those things remain; only the stuffiness is gone.

Volvo once seemed to think that its "typical buyer" -- 38 years old, parent of two, household income of $60,000 -- gave up all the fun and wildness after settling down. The 740 Turbo is a welcome respite from that oppressively proper thinking.

Outstanding praise: The styling. Volvo has dumped its multilinear -- a crease here, a crease there, right angles everywhere -- approach. All of the 740 Turbo's angles and curves are in the right places, both for appearance and aerodynamic efficiency.

The interior is classic Volvo. But this is where tradition makes sense. There's no wasted space in this wagon, which seats five big bodies quite comfortably and can tow over a ton and a half.

As usual with Volvo, the things that really count still count. Braking is superior. Safety belts are easily accessible both day and night, thanks to illuminated connections. (Why doesn't the government make all automakers light their seat belts?)

Outstanding complaint: I had to yield the 740 Turbo to the next test driver.

Ride, acceleration and handling: Excellent, excellent, excellent. The go comes from a 2.3- liter, four-cylinder, fuel-injected gasoline engine boosted by a turbocharger that increases compression and efficiency.

The turbocharger, by California's Garrett AirResearch, is said to be one of the most reliable and most easily maintained on the market. Because turbocharged engines are complicated, buyers really should read the manual.

Head-turning-quotient: This beauty attracted lots of attention.

Sound system: Not terribly exciting, but not terribly boring, either.

Mileage: About 24 to the gallon, combined city-highway, running lightly loaded and with climate control on "economy" most of the time. The 740 Turbo is equipped with a four- speed manual transmission with push-button overdrive. Unleaded fuels only.

Price as tested: $21,030, including a $320 shipping charge. All equipment is standard on this model.