The Civil Aeronautics Board yesterday approved an Eastern Airlines' fare plan that will allow two or more persons traveling together anywhere on Eastern's routes for $299 each.

Beginning Aug. 27, travelers will be permitted to buy a $299 ticket good after Sept. 11 that will enable them to make as many stops as they choose - but at least three - on Eastern's 105-city route system in the United States, Mexico, Canada, Bermuda, and the Carribbean during a 7-to 21-day trip.

The itinerary must be set, and the tickets purchased, at least 14 days before the trip begins.

Eastern also will allow one adult to travel on a $299 ticket accompanied by two or more children whose tickets will cost $199 each.

Although travel on this discount fare plan will not be permitted on certain days during holiday periods, the fare plan could be used around holidays with careful planning, an Eastern source noted yesterday.

The blacked-out days are Nov. 22, 23, 27 and 28. Dec. 21 through 26. Dec. 31 through Jan. 3. Feb. 15 throuhg 19. Feb. 24 through 27. March 17, 18, 23, 24, and 27, and April 1 and 2.

The CAB approved the discount plan, which is similar in concept to the Eurailpass available to travelers on European railroads, and packages offered by Amtrak and major American can bus companies.

The CAB also approved Eastern's proposal to liberalize existing individual tour fares to Florida. Discounts ranging from 25 to 40 per cent below regular coach fares will be available from many northern and midwestern cities - including Washington and Baltimore - on much less restrictive terms. For example, these fares would be allowed on weekends, the minimum stay requirement reduced from six to three days, the minimum expenditure required for ground services such as hotel cut from $60 to $45, and the advance purchase time lessened from 14 to 7 days.