Sweden's No. 2 doubles team today gave 18-year-old Boris Becker a playing lesson at no charge. The cost was borne by West Germany, which fell behind, 2-1, in the Davis Cup final.

The West Germans now must win both of Sunday's singles matches to capture the Davis Cup for the first time, and only the most irrational victims of Beckermania believe they can do that. Mats Wilander faces Becker and Sweden's Stefan Edberg plays Michael Westphal of West Germany in the last match.

Wilander and Joakim Nystrom administered a doubles defeat so crushing that the crowd hardly had a chance to cheer. The score was 6-4, 6-2, 6-1, and the last two sets were embarrassing to the West Germans. At the end of the second set and beginning of the third, they lost 13 straight points and 28 of 30. The match lasted 1 hour 18 minutes.

Andreas Maurer, Becker's partner, lost five of the six games he served, two of them at love. That is simply not supposed to happen in big-time doubles.

Adding to the humiliation was the fact that Wilander and Nystrom were substituting for Sweden's best pair, Anders Jarryd and Stefan Edberg, because Jarryd has tonsilitis. The substitutes never had played together in Cup competition, although they have an excellent record in major tournaments.

"Mats and I have always played doubles for fun," Nystrom said Friday. "Tomorrow it won't be fun."

It wasn't, for the West Germans. The Swedes returned serve perfectly, with Nystrom slapping Becker's big first serve for repeated winners. They proved much more adroit at the net -- "always one thought ahead of us," as Maurer put it. And Nystrom's serve, thought by some unequal to this task, never was broken.

The Swedes exposed the shortcomings of this West German team. Maurer, 27, is a steady, smart player with a weak serve. As he explained candidly after the match, "I've always had difficulty getting my service through. I usually volley pretty well behind it, but when they return as they did today, I can't do much volleying."

Although Becker can be intimidating on the doubles court, he lacks even the limited consistency he shows in singles. Each ace, blazing forehand winner and overhead bounced into the crowd is matched -- or more -- by mis-hit returns, double faults and flubbed volleys.

Maurer and Becker played as if they barely knew each other; Wilander and Nystrom moved like a dance team, seldom out of position, always choosing the right shot, never overhitting.

Given the intensity and hype that have accompanied this Davis Cup final, the doubles result had a stunning effect. Becker was so upset that he argued heatedly over line calls and even berated the net judge for calling one of his serves a let. After the match, he said sourly that one of the Swedish shots called good "would have been out in Sweden."

Becker, No. 6 in the world and the 1985 Wimbledon champion, said he was bothered by a torn muscle in his left side, an injury suffered in training last week. "I thought I wouldn't even be able to play the doubles, but they worked on it and I felt better before the match," he said. "I think I'll play Sunday."

Even if Becker returns to the hero's role and beats Wilander Sunday to tie the final at 2-2, West Germany's overall prospects are not good. Westphal, its second singles player, is not considered a serious threat to Edberg in the fifth and final match.