Boston — When it comes time for Vermont sheep farmer Henry Mosely to do his weekly weighing, he no longer faces a time-consuming two-day process. No more long evenings with pencil and paper figuring out which sheep have lost weight, and no roaming the fields the next day in search of the offending animals. Instead, he sits down with his terminal, punches in the sheep's weight as it registers on the scales, and lets his minicomputer tell him instantly if the animal needs attention.
Mr. Mosely is one of hundreds of farmers nationwide who now use computers for assistance with farm chores ranging from financial planning to livestock management.
The rapid growth in farm computer use is being spurred by input from several sources, including:
* The Kellogg Foundation, which is the major contributor to institutions providing farm-computer services. It has provided a $1.5 million grant to help establish the North Central Computer Institute in Madison, Wisc. Scheduled to open on Jan. 1, l982, the institute will serve as a clearinghouse for farm-related computer information.
* Land-grant universities and colleges. The extension services of these institutions, which to extend educational opportunities to rural dwellers, have taken the lead in bringing computer technology to the farm. Computer networks now in operation across the country provide computer service to farmers for a user's fee.
* Private industry. Although the mini-computer was not aimed specifically at farmers, programming entrepreneurs spotted the promising sales figures of home computers and compiled a number of agricultural programs that now fill the software catalogs of major home computer manufacturers.
Though some farmers employ computers strictly for financial management and tax analysis, they are not limited to calculations. The computer can also perform functions never before possible, in the sense that it can manipulate many more variables than a farmer could ever hope to remember.
In the case of sheep farmers, for instance, the computer can keep track of woolweights, rate of growth, birth rates, and many other statistics, and then score the animals - predicting their future profitability, telling when the animals should be bred, and so on.
The extent to which computer use has caught on varies widely from region to region. According to Dr. William Shimmel, director of the University of Vermont extension service, virtually every agricultural state now has an extension program experimenting with computers, but some are much farther along than others.
Dr. Robert Kramer, program director for agriculture at the Kellogg Foundation , predicts that 90 percent of the county extension offices nationwide will be equipped with computers by 1990. The figure now stands at less than 20 percent. He also says that by l990, 75 percent of those farms in the US that anually sell between $20,000 and $125,000 in agricultural products will be utilizing computers in all aspects of their operations.
The lack of relevant software (prepared programs) for both home computers and those at the regional centers is slowing the growth of farm computer use. Home computer programs are often general in nature and directed to the computer hobbyist, not the typical farmer who lacks the expertise to alter a program to his own specific needs.
Dr. Thomas Thompson, professor of agricultural engineering at the University of Nebraska, says he forsees the evolution of a system combining the functions of small, farm-based computers with those of larger ones at regional computer centers.
He predicts that by 1990 the majority of commercial farms in this country will have mini-computers for nerve centers, with microprocessors (terminals) at various locations around the farms to serve as electronic ''note pads.'' The mini-computer also could be linked to computers at regional centers around the country and receive weather data, commodity prices, and other information.
Private industry has done little research and experimentation in farm computer technology, limiting its role to selling hardware and software. The exception is Rural Venture, a private firm that has launched a pilot project to revive sheep farming in New England with the help of computers.