HILTON INTERNATIONAL has launched two-for-one weekend rates at hotels in 19 European cities and in Cairo. Through March 30,1990, guests can stay in a participating hotel Friday and Saturday or Saturday and Sunday and pay the cost of one night. A third night is half-price.

The hotels are in Amsterdam, Anakara, Athens, Basel, Brussels, Cairo, Cyprus, Dusseldorf, Geneva, Istanbul, Mainz, Malta, Milan, Munich, Paris, Rome, Rotterdam, Strasbourg, Vienna and Zurich. Reservations: 800-444-8667.FAIRMONT HOTELS, in San Francisco, San Jose, Chicago, Dallas and New Orleans, are now offering weekend rates of as much as 60 percent off of weekday prices. In Dallas, New Orleans and San Jose a room is $79 a night. In Chicago a room is $99, and in San Francisco, $145. For an additional $20 a room can be upgraded to a suite. Reservations: 800-527-4727.

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On March 15, Amtrak changed some of its fares, with some long-distance fares going up as much as $30 and others going down as much as $44. The shifts followed Amtrak's changing the way it codes its fares for ticket agents.

The increases are mainly in the All Aboard America fares, which apply through May. The fare for travel in one region of the country went up to $179 from $149; for two regions to $229 from $199, and for three regions $259 from $249.

New York to Miami is now $142 one way, down from $186. New York to Tampa one way is now $142, down from $184. Fares between New York and Washington and New York and Albany are unchanged.

Reservations or ticketing made before March 15 will not be affected.

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The 13th Spoleto Festival U.S.A. runs from May 26 to June 11 in Charleston, S.C.

Tickets are $8 to $45. For a brochure with forms for ordering: Spoleto Festival U.S.A., Post Office Box 157, Charleston, S.C. 29402; 803-722-2764.