If you were to check around town to find out how different youngsters pass their spare time, you'd discover that 10 of Washington's most popular and important outlets for constructive youth energy are the units of the Metropolitan Police Boys' Club. Today, some 22,000 youths from all neighborhoods are members of this club - whose ranks in years past included Walter E. Fauntroy, Maurice J. Cullinane and 170 current officers in the police department.

Yet after 43 years of club operations, all but the newest one of these bustling centers are in pitiful physical shape; and even if they were in tip-top shape, there would not be enough of them to fill the need. That is why we wish to take note of a most important campaign now under way to raise $5 million for the construction of eight new clubhouses. If you think, as we do, that it's worth trying to help combat juvenile deliquency, while generally promoting good citizenship and bridging the generation gap, then you will agree that a contribution to the clubhouse drive is an excellent local investment.

We would have preferred, however, for this response to materialize without any door-to-door solicitations by uniformed police officers, such as Chief Cullinane is permitting. The chief, understandably proud of his department's commitment to the club over the years, has made a once-only exception to the ban on such activity that was ordered by his predecessor, Jerry V. Wilson. We have long believed that no matter how worthy the cause, door-to-door solicitation by uniformed police officers creates an impression - however unintended - of pressure from law-enforcement authorities to pay up. This year's police solicitation, even though limited to business establishments, should be dropped.

We hasten to emphasize that this point shouldn't be a basis for withholding contributions. Nor, we might add, should the name of the organization be taken literally by those who might take offense at its suggestion of sex discrimination. The name probably should be changed for appearances sake, but the fact is that the club's centers are used by boys and girls.

Moreover, though athletics continues to be the heart of the club's activities, there are excellent tutoring programs and a fine summer camp. As Chief Cullinane has commented, the campaign is not just to build buildings. The purpose is to expand a proven program designed to build people who will contribute substantially to the well-being of this city. 'Aweigh Day'

You're invited to see for yourself this weekend, but word has it that marine experts have actually found signs of life on Washington's Maine Avenue waterfront. Not a genuine bustle, mind you, but sufficient to raise the possibility of a lively, people-and-boat-filled spring and summer season along the water's edge. At least that's what a new, non-profit group of waterfront restaurateurs, businesses and other organizations such as Arena Stage and the Disabled American Veterans are setting out to prove through a festive "Aweigh-Day" of free activities for the public all day today.

It really shouldn't be all that difficult to prove, for is a bit stiff - has always been a natural for pleasant family activities. The problem has been that until now, no group mobilized to focus attention on this area. The new federation, calling itself the Waterfront Washington Association, has organized to do this under the interim chairmanship of James P. Alexander, popular former city government executive.

So from 11 a.m. to 8 p.m., the waterfront is scheduled to come alive with art, handiwork, musical groups, dancing, a parade of boats, the blessing of the fleet and open houses aboard many craft. Mr. Alexander also advises that the "First Annual Molly Malone Fish Mongering Contest" will be held at about 4 p.m., not long before an "alert" is to be conducted to see if the monster in the Tidal Basin can be spotted; legend has it, or at least Mr. Alexander does, that if this benign monster is sighted, an enjoyable boating season is assured. At any rate, this good-natured fun is the first in a series of special days over the coming months. In hopes of a festive waterfront year 'round, we wish the effort smooth sailing. The Fare Foul-Up

If you think that coming up with exact change for the bus or subway is a nuisance, consider what you may confront come July, when 12 more miles of Metrorail are scheduled to open and when hundreds of bus routes are to be shifted to serve the new rail system. It wouldn't be so bad if the Metro board hadn't failed to meet its own deadline last week for setting new fares to go into effect then. The board can still effect the new fares - but failure to approve the new rates now apparently means they won't be listed on the new bus schedules being printed.

That may not seem so catastrophic - especially if you always travel with a computer, protractor, celsius table and maybe even a bag of lunch. The proposed subway fares call for 40 cents for the first three miles, with extra miles at 3.75 cents each except during rush hour when it would be 7.5 cents - all of this, of course, rounded off to the nearest nickel (or is it the nearest station?). Oh, yes, and there's to be a new fare schedule for people riding bus and subway in the same trip, and it's a different fare in different directions. Finally, there will be new automatic fare collection equipment in the subways to charge riders by the distance traveled. Information on this new wrinkle, as we understand it, will be contained in those brochures that won't tell you the new fares. Clear? Then you may turn in the special pencil to your instructor.