Citing "the urgent need to reduce the federal budget," the Agriculture Department has canceled a four-year-old emergency program to help farmers buy feed for livestock when natural disasters reduce their crops.

Under the program, eligible farmers and ranchers could be reimbursed for up to 50 percent of the cost of buying additional feed when their crops were ruined by floods, drought, fire, hurricane, earthquakes or storms.

Since the program started in fiscal 1978, it has disbursed $590.2 million.

The cost of the program varies widely depending on the weather. In fiscal 1980, the department spent only $23.4 million to help 11,525 farmers, but in fiscal 1981 it spent $328.5 million for 136,721 farmers. Since last October, the department has paid out $5.7 million.

The department formally ended the program with a notice in the March 9 Federal Register. In the notice, USDA said it would accept applications for the program through April 8, but not for losses occurring after March 9. Clarence Domire, a USDA program specialist, said that this was "the slowest time of year for the program."

Under the program, the secretary first determined that an emergency existed in a certain area. Then farmers could qualify if they had suffered a "substantial loss" in the feed they normally produced for their own livestock, that they did not have sufficient feed for their livestock for the estimated period of the emergency and that they needed to make feed purchases larger than he normally would.

In its notice, the department noted that since the program is "discretionary," the secretary can reinstitute it if an emergency exists that "warrants such implementation."