Republican presidential candidate Ronald Reagan predicted today that President Carter would propose a tax in October, but said the American people "won't be fooled by an election-year conversion."

Resuming campaigning after cinching the GOP nomination, the former California governor opened a three-day swing through Ohio at a late afternoon rally in Fountain Square here.

Despite the efforts of Ohio Gov. James A. Rhodes and the GOP organization, the visit drew not more than 2,000 people at 5 p.m., when nearby office buildings were emptying of workers.

Reagan, who flew in from California, told the crowd that Carter will change his tune about tax cuts being "inflationary" as the election draws near. c

"I bet you, along about October when we get closer to the election, he'll begin to see the virtue of a tax cut," Reagan said.

Carter has opposed tax cuts this year, but has held out hope of a reduction in 1981 after the budget has been balanced and inflation brought under control.

Reagan ridiculed the president's logic and his claims for progress in the war against inflation.

"He says inflation has dropped from 20 percent to 16.4 percent for the last four months," Reagan said. "But it's still four times as bad as it was when he became president."

"Interest rates are down, he says," Reagan continued, "but they are still three times what they were when he took office."

The former California governor was given a lavish introduction by Rhodes, who had endorsed him for nomination in mid-April after seeing his original favorite, John B. Connally, go down to defeat.

Rhodes called Reagan, "a man of strength and compassion, who cares first about America's working people and their families."

Reagan said that Rhodes had given him "an introduction I would be hard put to live up to."