International Harvester Co., the troubled farm equipment and truck manufacturer, has reached a new agreement with the United Auto Workers that apparently will save the company at least $100 million through September and nearly that much again through 1984.

Neither union nor Harvester officials would comment on the terms of the new labor agreement until it is submitted to the 30,000 rank-and-file UAW members who work for Harvester. A union spokesman said the new agreement, which would replace the current pact that is scheduled to expire Sept. 30, will be submitted to the membership "as soon as possible," perhaps by this weekend.

Harvester lost nearly $300 million in its first quarter that ended Jan. 31. The company lost $393.1 million and $397.3 million in its two previous fiscal years, which end Oct. 31.

Tuesday, Harvester's bankers agreed to ease the terms of a $4.2 billion loan agreement hammered out only last December, and Harvester officials have said they will need further concessions from the banks because of its difficult financial position.

Harvester asked the UAW for contract concessions last November, but the union broke off talks early this year after Harvester paid $6 million in bonuses to white collar workers. But talks resumed three weeks ago after Harvester's position continued to deteriorate. Sales fell 33 percent in the first quarter.

Harvester said yesterday that it will begin to recall 4,150 laid-off workers next week when it reopens its tractor plant in Rock Island, Ill. Other workers will be recalled at plants that supply parts to the Rock Island facility, which has been closed for two months.

Harvester spokesman Bill Colwell said there is no relationship between the new union settlement and reopening of the tractor plant.

International Harvester was weakened first by a six-month strike in 1979 and 1980. By the time the inconclusive strike was settled in April 1980, Harvester's main customers were buffeted by a recession and high interest rates.