Several hundred legislators and governors from 15 midwestern states descended on Congress yesterday in an unusual lobbying effort to break loose more federal aid for their troubled farm economies.

The barnstorming lawmakers, including the entire 105-member South Dakota legislature, found sympathetic ears, but they got little more than sympathy from Reagan administration officials.

Agriculture Secretary John R. Block told a panel of the National Governors' Association that the administration would add more money to its farm debt-restructuring program if needed. But he renewed a call for states and commercial banks to act more forcefully on their own to solve rural problems.

Block's call drew protests and grumbles from some governors and legislators, typified by South Dakota Gov. William Janklow (R) who said that "to take on the federal burdens will drag the states down."

Earlier in the day, Janklow charged that the federal government's farm policies are "destroying a basic industry" and that Washington politicians are spending too much time trying to score points.

"Frankly, I don't care whose fault it is," he said. "You folks in both parties and the administrative branch have to have the courage to stop posturing. If this were 200 years ago, people would be dumping tea in the Potomac."

Nebraska Gov. Robert Kerrey (D), whose agriculturally dependent state is under intense pressure from low prices, high interest rates and falling land values, expressed bitterness about the refusal of Sen. Jesse Helms (R-N.C.) to convene the Senate Agriculture Committee to meet with the visitors.

Kerrey and several dozen other witnesses from the Midwest testified at a "non-hearing" called by Sen. Edward Zorinsky (D-Neb.), ranking Democrat on the agriculture panel, to give the state legislators a forum for describing what they uniformly called an economic crisis in rural America.

The Nebraska governor said Helms' refusal was "an affront to the entire 15-state delegation." Later in the day, at the National Governors' Association, Kerrey took Helms to task for lecturing them on "posturing."

"We don't even need to have hearings; we know what the problem is," Helms said. "I hope I will never be guilty of posturing on the plight of the American farmer."

After Helms left the standing-room-only meeting of the NGA agriculture panel, Kerrey said Helms was posturing and "not exactly encouraging bipartisanship."

While the administration continued to maintain that its debt-restructuring program would prevent many farmers from going bankrupt this spring, Senate Democrats and a few GOP allies continued their push to force a vote on amendments to broaden the program.

Amendments to an African famine relief bill by Zorinsky and Sen. Alan J. Dixon (D-Ill.) picked up Republican cosponsors, although Majority Leader Robert J. Dole (R-Kan.) warned that he did not want to see farm-state Republicans pushing more amendments.

They would further liberalize terms for a credit-relief program implemented last week and advance payments for price-support loans from the fall to the spring.