UNITED STATES TICKETS FOR THE SUMMER OLYMPICS in Seoul will go on sale shortly from California-based Olson-Travelworld Ltd. In Canada, the Seoul Travel Service in Toronto has already begun selling tickets. Both agencies are now in the process of developing complete Olympic travel packages, including air transportation, accommodations, game tickets, and sightseeing tours. Olson-Travelworld can be reached by calling either 800-421-2255 or (213) 670-7100. Canada's ticket service number is (416) 535-6004. More travel information is available through Korea National Tourism Corp., 460 Park Ave., New York, NY 10022; (212) 688-7543. VIDEO CHECK-OUT SYSTEMS ARE NOW BEING USED by more than 190 US hotels, reports Travel Agent magazine. Guests can call up their bills any time on the video screen, verify changes, and check out without stopping at the front desk. The new technology also offers video messages and video breakfast menus. Research into faster check-in service includes the possibility of checking in at an airport or car rental outlet, and use of credit card scanners that ``read'' card information. MORE AMERICANS ARE TRAVELING TO THE SOVIET UNION, reports the Russian Travel Bureau. In the last three months, records have been set for inquiries and advance bookings. Because of the limited number of first-class hotel accommodations there, the bureau suggests making reservations well in advance.