Republicans abandoned the administration in a massive way yesterday as the House passed a $2 billion emergency farm credit bill by a sweeping vote of 378 to 35.

The Reagan administration had opposed major sections of the bill, aimed at providing more Farmers Home Administration loan assistance to farmers plagued by low prices and heavy debt, but only 27 Republicans voted against final passage.

Among the Republicans who voted in favor of the bill were House Minority Leader Robert H. Michel and fellow Illinoisan Edward R. Madigan, ranking minority member of the Agriculture Committee, who first forced Democrats to compromise on several key issues. The bill is intended to boost and liberalize credit available to the 12 to 15 percent of all farmers who cannot borrow from banks and look to FmHA for operating loans each year.

Earlier yesterday, House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) cited Republican actions on the farm-credit bill during floor consideration last week as a prime example of GOP obstruction of a series of Democratic recession-aid measures. But House Democrats, faced with the possibility of weeks of GOP delaying tactics and time-consuming roll calls, decided to take what they could get yesterday and push the farm credit bill through to final passage, albeit with some changes sought by Madigan, who represents a relatively prosperous grain district.

Among the major changes:

* Although the bill would reactivate a defunct economic-emergency loan program, against administration objections, the Republicans were able to cut the authorization level from $1.2 billion to $300 million in fiscal 1983 and to $600 million in fiscal 1984.

* The agriculture secretary still would have final say on extension of a delinquent farmer-borrower's credit, but Madigan forced the Democrats to accept language that put more of a burden on the farmer to prove his case for extension.

In the end, according to Rep. Ed Jones (D-Tenn.), rural credit subcommittee chairman, who was a chief architect of the farm-assistance package, the Democrats had little choice but to compromise with planting season at hand.

"There's no question, this would have gone on for weeks, but we needed a bill now and we needed a bill that the president would sign," Jones said. "It's time to get the money out there. People are being hurt and sold out every day. These farmers can't get money elsewhere and without this, they won't have a crop this year."

The administration gave no hint yesterday about its position on the amended measure. Jones said that Department of Agriculture representatives did not take part in behind-the-scenes negotiating between opposing forces. "We just don't know where they stand," he said.

The bill now goes to the Senate, where a counterpart, although passed by the Agriculture Committee, has been trapped in a legislative logjam on the floor for weeks, with no signs of breaking loose soon. The House bill, pushed by Jones and Rep. E. Thomas Coleman (R-Mo.), was designed as quick-fix assistance for tens of thousands of the FmHA's 270,000 borrowers with delinquent loans and poor recovery prospects because of low commodity prices and high operating costs.

Its most controversial section--opposed adamantly by the administration--would have required the secretary to extend special repayment consideration to delinquent borrowers who had good management records and could show that they were in arrears through no fault of their own. Secretary John R. Block has argued that FmHA already is following such a policy, and while the compromise would require the agency to continue on that course the borrower would have to show solid evidence of being able to succeed if given federal loan assistance.