CAPE CANAVERAL, Fla. (AP) _ The planet's two space superpowers already have exchanged handshakes and hugs, shared borscht and cranberry sauce, and toasted with apple juice - 140 miles above Earth.

This week, 19 years after the Apollo-Soyuz docking mission, five American astronauts and one Russian cosmonaut will pick up in orbit where their predecessors left off.

Sergei Krikalev will become the first Russian to fly on a U.S. space shuttle when Discovery lifts off Thursday on a science mission.

Unlike Apollo-Soyuz, which brought three Americans and two Russians together in orbit in 1975, astronauts and cosmonauts will occupy the same ship from launch through landing.

''This to me is a real landmark, not just because Sergei's on our flight, but because our two countries are working together,'' said Discovery astronaut Jan Davis.

Both countries say the mission is only the beginning of many joint space ventures.

The ultimate goal is an international space station, to be built using launch vehicles from both countries. Construction is scheduled to begin in 1997 and the station is expected to house permanent crews by 2001.

The two countries agreed on the joint station late last year. They also agreed to 10 shuttle dockings with Russia's Mir space station, beginning in 1995, to exchange crews, do research and upgrade the aging Mir.

The deal expanded on a 1992 agreement that arranged for Krikalev's flight and for an American astronaut to fly on Mir for three months in 1995.

Altogether, five American astronauts are to spend a combined 24 months on Mir. And another Russian cosmonaut - Vladimir Titov, Krikalev's backup for Discovery's mission - already is training for a shuttle flight early next year.

NASA has trained Krikalev and Titov as full-fledged shuttle crewmen since their arrival in November 1992. Both are pros: Krikalev already has spent 463 days in space and Titov 368 days.

''What is most interesting part of this mission for me is flying on space shuttle itself,'' Krikalev said. ''I have long period of time flying on Mir station. I flew on Soyuz vehicle. But this is new vehicle, new hardware, new experiments.''

Marcia Smith, a specialist in space policy for the Congressional Research Service at the Library of Congress, said the cosmonaut and astronaut exchanges make for good foreign policy.

But she said it's risky to build a space station with the Russians given the country's political and economic instability.

''Apollo-Soyuz was not supposed to be a one-time deal. It was supposed to be a new era of detente. It was supposed to lead to other things ... but it never did lead to anything at that time,'' Smith said. ''The same thing could happen again.''

Krikalev has the crucial job of using Discovery's robot arm to retrieve a satellite deployed by the crew during the eight-day mission. The satellite, called the Wake Shield Facility, is being flown to see if it can create an ultravacuum for growing thin, pure semiconductor films.

Krikalev also will help conduct experiments in a pressurized module called Spacehab and take part in joint U.S.-Russian investigations involving radiation, physiology and Earth observations.

Whatever the results of the Discovery mission, Commander Charles Bolden Jr. already considers it a success.

''People talk about joint U.S.-Russian this and that. If we don't get people to be able to trust each other first of all, one on one, we're not going anywhere,'' Bolden said. ''And so I think that's been the most important achievement of our flight.

''If we go out and Wake Shield doesn't work and Spacehab doesn't work, that will be a great disappointment. But this preceding year, I think, stands on its own merits.''