Education Secretary T.H. Bell used to be the 97-pound weakling of the Reagan Cabinet. His chief job was to abolish his job. He failed.

Now suddenly Bell has become a Cabinet heavyweight. The secretary rides on Air Force One with President Reagan, appears on Meet the Press, and receives standing ovations on the mashed-potato-and-fried-chicken circuit. People actually seek out his autograph.

Bell "holds the most important job in America next to the president today," Frank Fahrenkopf, chairman of the Republican National Committee, declared last week in Dallas.

The hyperbole had a nice ring for Bell. "That was a little strong for someone who is number 13 in the Cabinet, and maybe a long way behind number 12," he said later. "But I didn't mind hearing it anyway."

Short, unassuming and snowy-haired, he is an unlikely administration hero. It is hard to imagine a quicker transformation. During his first two years in office, Bell was chastised by Congress, denounced by the education community and largely ignored by the White House as the Reagan administration slashed education spending and tried to eliminate his department.

The National Commission on Excellence in Education abruptly changed his stature. Bell formed it soon after his confirmation. He had consulted with the White House about the commission, but administration officials had pretty much forgotten about it by the time the commission asked to meet with Reagan to give him its final report. The initial reaction was to say no.

But, according to sources, Michael K. Deaver, deputy White House chief of staff, became interested in the report, which found a "rising tide of mediocrity" in American education. He asked Edward J. Rollins, the White House political director, to look at polling data on education issues.

The polls revealed a deep undercurrent of concern about the nation's schools. The commission was invited to present its report, "A Nation at Risk," to the president.

An "instant issue" was born. The White House, looking for a domestic issue for the president, seized it. Speeches were written, appearances arranged.

"This issue hits across our constituency groups. The majority of people in the country feel it's time to put discipline and excellence back in our schools," Rollins said. "The 1984 election isn't going to be won or lost on education, but there's no question it will play a part."

MONDALE AND MERIT PAY . . . To the Democrats, the whole thing smacked of political opportunism. The administration's education policy had been centered on eliminating the department, legalizing prayer in public schools, enacting tax credits for parents with children in private schools, and reducing the federal role in education.

Walter F. Mondale, the frontrunner for the Democrats' 1984 presidential nomination, was the first to strike, proposing an $11 billion education program. Reagan strategists had hoped for just such a reaction. They saw it as a golden opportunity to take an early swing at the former vice president, and connect him with the National Education Association, the nation's largest teachers union.

By this time, the administration was concentrating its support on one commission recommendation--merit pay for teachers, something long opposed by the NEA. Bell had first fought the NEA over merit pay back in 1961 during his days as a county school superindentent in Ogden, Utah. He became a willing point man in the new attack, blasting Mondale and the NEA last week.

"I won't call this political opportunism so much as I'd call it a major public policy debate," Bell said in an interview. "The more we can have a high-level debate about education, and how to improve it, the better off education will be."

BACK AT THE DEPARTMENT . . . With the new focus on education, the administration has unofficially abandoned its effort to get Congress to abolish the department.

Meanwhile, staff morale is "very low, primarily because of confusion over the mission, direction and future of the department," according to a task force that studied how to cut government costs.

A report by the President's Private Sector Survey on Cost Control said the department was poorly managed and top-heavy with high-level staff members. Reagan, it added, has made matters worse by doubling the number of the department's presidential appointees, few of whom have "the business experience and management expertise needed to run a large financial institution."