The American airlines that participate in a strike insurance pact have agreed to cut back sharply on the benefits paid to struck airlines in order to eliminate the possibility that an airline could show a profit while on strike.

The action comes as the agreement - Called the Mutual Aid Pact (MAP) - has been under increasing attack during the lengthy airline pilot's strike against Northwest Airlines.

During the 109-day strike, member airlines gave Northwest about $108 million for an average of almost $1 million a day. The Airline Pilots Association, which has been highly critical of the MAP, contends that Northwest, an efficient, low-cost operator, made a profit during its strike.

Representatives of airlines participating in MAP met in New York last week and agreed to cut the guaranteed benefits payable under the agreement by about one-third and to eliminate guaranteed payments altogether after the first 10 weeks of a strike.

Currently, an airline being struck gets 50 percent of its daily operating expenses for the first two weeks, 45 percent the third week, 40 percent the fouth week and 35 percent for the remainder of the strike.

Under the changes agreed to by the 15 airlines, a carrier would be reimbursed for 35 percent of its normal operating costs during the first two weeks of a strike, 25 percent for the next eight weeks and nothing after that.

The airline did not alter a provision of the pact under which airlines that experience increased business because of a strike give their increased net revenues to the struck carrier for the duration of the strike.

The pacr - which expired in February - is being reviewed by the Civil Aeronautics Board, which approved it in 1958 for the first time and every five years since. There is also increased criticism of the pact in Congress, where an amendment to abolish it is expected to be introduced during debate on airline deregulation legislation.