In Martinsburg, W. Va., where President Carter went last Friday seeking grass-roots opinion, his host, Marvin Porterfield, called the president's speech "the strongest I've heard him deliver."

"Heaven only knows how the public will respond. . . but the president needs an enlightened Congress and an enlightened electorate. I think we're going to shape up. He touched a nerve."

Porterfield said he an his wife recognize little in Carter's address that came directly from their session last Friday. They and 15 other persons from Martinsburg drank coffee and tea and ate cookies with the Carters during the 90-minute meeting.

"I would hate to claim I had an input in anything the president said," Porterfield said. "But he did touch on one of the topics that came up here, whether the government or the corporations should play the main role."

Porterfield said everyone had "a grand time" and that Carter impressed most of the guests.

"I feel stronger about him than I did before. He's a sincere fellow, but he has been handicapped by the advice he has been given. . . I expressed the thought that he is a poor judge of horseflesh - an absurd number of his closest advisers are from Georgia. We felt he should be seeking the advice of the finest minds available." CAPTION: Picture, Marvin and Virginia Porterfield of Martinsburg, hosts to President Carter. AP