The Civil Aeronautics Board yesterday raised the maximum fares that airlines can charge on overseas flights and blamed the increases on the soaring cost of jet fuel.

The CAB said fares can be boosted by 6.1 percent on flights to Latin America, 8 percent across the North Atlantic and 9 percent over the Pacific.

Most major airlines are expected to put the new higher fares into effect on most routes, effective April 1, when the new CAB maximums become official.

The aviation regulatory agency said the fare hikes were necessary because the price overseas airlines pay for fuel is rising about 1.55 cents a week. The airlines are now paying between $1.07 and $1.16 a gallon for jet fuel.

The fare increase is the second in the last six months and the first ordered by the CAB under a new federal law that went into effect Feb. 15. The International Air Transportation Competition Act requires the agency to set a standard foreign fare level and to adjust it to reflect airline operating costs.

Fares went up before the new law went into effect. Counting the latest increases, the maximum fares have jumped 11.9 percent on Latin American routes, 14 percent on Atlantic crossings and 17.2 percent on Pacific flights since last October.

Airlines cannot charge more than the maximum rates set by the CAB for coach-class seats and can offer discounts of up to 50 percent from the ceiling fare.

CAB sources said fares are now at the maximum levels on all but the most competitive international routes. Discounts are generally available on the New York-to-London and New York-to-Amsterdam routes, where several carriers are vying for business.

Under the new rate-setting system, the CAB will review fares every couple of months and probably will increase fares again in June unless fuel costs stop growing.

The CAB action to raise fares comes at a time when some airlines are beginning to offer new discounts to encourage travel on long trips.

Pan American world Airways on Monday began giving discount coupons, good only on overseas flights, to passengers who fly between Washington or New York and Florida on National Airlines.

Pan Am acquired National earlier this year and the promotion is the first effort to use National to stimulate Pan Am's overseas business.

The Pan Am coupons allow passengers to buy two tickets for the price of one on flights from the United States to a limited number of foreign destinations, including Germany, Australia, Thailand, Hong Kong and Kenya.

World Airways, which flys, a special economy-class service from the East Coast to California and Hawaii, also has launched a discount coupon, offering reductions of $50 from its usual fares.