Canada Offers Birthday Bargains for Its 125th : Airlines, rail system, youth hostels offer special discounts for summer travelers.

In honor of Canada’s 125th birthday, Canadian Airlines is offering a special youth fare called Canada 125.

Canada 125 fares are valid on all Canadian Airlines flights within Canada through Sept. 9, for travelers ages 16-21 (proof of age is required). However, the special fares are only offered on a standby (space-available) basis.

Under the Canada 125 program, all “long-haul� flights--1 1/2 hours or longer-- are priced at about $106 U.S. one way, or $212 round trip. “Short-haul� flights--those which take less than 1 1/2 hours--are available for $53 one way, $106 round trip. Check with the airlines or a travel agent to clarify.

In addition, Canadian Airlines continues to offer its regular standby youth fare, available year-round to travelers 12-24. The rates are not as low as the Canada 125 fares, but the tickets are valid for a full year after purchase.

Another Canadian airline, Air Canada, also offers domestic youth fares, year-round, for travelers under 25 who are willing to travel standby.

Air Canada’s regular one-way economy fare between Montreal and Toronto is $175, while the youth fare is $61. A round-trip economy fare, with advance purchase, between Vancouver and Toronto is $298; the youth fare is $203.

For those who prefer to cross Canada by train, VIA Rail offers some special breaks for students and other young travelers. Full-time students, for example, are eligible for a 10% discount on rail travel within Canada at any time.

Special youth rates are available with VIA Rail’s Canrailpasses. The Canrailpass is valid for unlimited coach-class travel on any 12 days within a 30-day period.

The regular high-season Canrailpass (valid through October) costs $373. Youths (24 and under) and seniors (60 and older) can purchase the pass for $339. All pass holders also have the option of paying extra for on-board sleeping accommodations.

Travelers searching for low-cost lodging in Canada this summer will be able to take advantage of more than 60 youth hostels operated by the Canadian Hostelling Assn.

The pride of the system is the spectacular Lake Louise International Hostel, located in the Canadian Rockies about a two-hour drive from Calgary. The hostel opened Jan. 1.

Members of affiliated hostel associations, or of the Alpine Club of Canada, are charged $13 (plus tax) per person, per night, to stay in a room shared by four to six people, or $15 per person to stay in a room with two beds. Non-members are charged an additional $4.25. The maximum stay is 10 nights. There are no age requirements.

In summer, the staff operates hiking and outdoor activity programs. During the winter, guests can ski cross-country or downhill; a free shuttle bus takes them to the lifts. For more information or reservations, contact the Lake Louise International Hostel, P.O. Box 115, Lake Louise, Alberta TO1 1EO, Canada; (403) 522-2200.