The Civil Aeronautics Board approved tough new rules yesterday to protect charter participants from last-minute undesired changes in flight and tour plans.

Under the new rules, charter travelers will be able to cancel their trips and get full refunds if the tour operator makes any "major" vhange in the trip as advertised. A change in the date or city of departure, the destination, or the hotels scheduled would be considered "major" under the new rules and entitle the participant to opt out of the trip and get a refund.

Passengers must be notified by the tour operators of any major changes at least 10 days before departure. If a change is made within 10 days of the trip, the passenger has to be notified as soon as possible. If a change occurs after the trip has begun, the passenger has a right to reject the substitution and get a refund for the portion of the trip that was changed.

If a charter participant is notified of a change 10 ot more days before departure, he or she has seven days in which to notify the operator that a refund is desired; a refund has to be sent within 14 days of being notified of the would-be participant's desire to cancel.

Although the tour operators will be required to give refunds for making major changes in advertised trips, the CAB did not remove the option of offering trips that leave some flexibility for the operators to fix the exact dates, destinations, departure cities and hotels after people have signed contracts.

But the operator must disclose all the possible alternatives in advertising and the written contract provided the potential traveler. The operator must notify the traveler of the cities and dates for the charter at least 10 days before the earliest of any of the alternative dates.

The CAB decided it would give a name to these flexible charters that would connote the uncertainty of their details to consumers in their advertising, but CAB members at their meething yesterday couldn't decide on a name.

The new rules will apply to contracts entered into 60 days from today for flights scheduled to leave 120 days from today. The timing is designed to give operators time to print the new contracts that will be required and to avoid interfering with contracts already signed.

Other provisions of the new rules.

Spell out type sizes for required disclosures in written contracts.

Bar an operater more from raising the price of a charter more than an aggregate 10 percent (the price can be increased only if the operator has specifically reserved the right to increase the price, and it has to be done more than 10 days before departure).

Prohibit an operator from collecting any money until a participant has signed a contract.