Of the 6,530 goals scored in the National Hockey League last season, 1,497 -- or 21.4 percent -- came on power plays, when a team enjoyed an advantage in manpower because of a penalty to the opposition.

Extra-man situations are the subject of constant practice because, in addition to the obvious gains from scoring a goal, there is great psychological risk from the inability to come close.

Shouts of "decline the penalty" from the home fans, accompanied by boos, can affect a hockey team harshly. Such has often been the case at Capital Centre, where an off-target pass or blocked shot incited displeasure last season despite the Capitals' No. 4 ranking in power-play goals.

The Capitals succeeded on power plays 23.9 percent of the time, as opposed to the league average of 22.2.

Perhaps the heights of power-play productivity were attained by Montreal in the mid-1950s. The Canadiens were so good they inspired a rule change -- until 1956 a minor penalty was served to its entirety no matter how many power-play goals were scored during the two minutes. Now, one goal ends a minor.

The rates of success have been declining in recent years for two major reasons. First, all teams routinely prescout opponents, either in person or on television, and they are aware of their preferences in extra-man situations. Second, the widespread use of offensive-minded forwards as penalty killers has tended to make many power-play units relatively timid.

The failure to adjust will doom the most successful power play. In 1983-84, Minnesota ranked No. 1 in the NHL. Last season it fell to 16th, in large part because opponents had learned what to expect. A few years ago, Washington enjoyed success by running offensive interference near the right post, thereby leaving a shooter open for a good shot. Eventually, opponents were waiting and nullified the maneuver.

The object of a team skating with one or two extra players is first to set up across the opponents' blueline and then to free a player for a high-percentage shot. Set plays often are used, with a basketball-type pick a common maneuver to prevent an opponent from deflecting a shot.

In a typical play, the wings will be in the faceoff circles with a big forward jamming the front of the net. One of the two point men will try to close in for a shot, while prepared to pass off to a wing if challenged.

Some teams like to have the point men fire away from a distance, hoping the jammer will either distract the goalie or deflect the puck past him. However, too often inexperienced point men have shots blocked, forcing their team to regroup or, at worst, hope their goaltender can foil a short-handed breakaway.

Most teams practice the power play in two units, each prepared to skate for about a minute, although such stars as Edmonton's Wayne Gretzky frequently skate the full two minutes.

If a team manages to force a faceoff in the opponent's ice, it usually will flip flop its wings, as in this situation the shooting angles are enhanced by a right-hand shot on the left side and vice versa.

A principal requirement of a power-play unit is patience. It may require 15 passes to obtain the desired shot and the complaints of anxious fans often provide a spur to hurry things up. Yet one good shot is enough; it beats five trips down the ice to regroup.

Another prime requisite is confidence, to the extent that coaches having power-play problems will practice with the penalty killers holding their sticks at the blades, to prevent them from demoralizing the offense.