Launching a final round of media salvos before Election Day, President Reagan and Sen. Edward M. Kennedy (D-Mass.) yesterday framed opposing Republican and Democratic arguments on the economy and the Social Security system as the 1982 midterm campaign drew to a close.

Speaking from the house of an unemployed auto worker in Massachusetts, Kennedy said in a morning radio address on behalf of Democrats: "There is no corner to be turned so long as we continue down the blind alley of Reagan economics."

In his weekly radio talk from Camp David, Md., Reagan said, "a careful study of the success of our existing policies in laying a groundwork for economic recovery will convince you they deserve more than the 13-month trial they've been given."

The radio appeals were to be followed by a weekend of five-minute television advertisements in which Reagan and former Democratic senator Edmund S. Muskie seek to sway voters at the conclusion of a campaign in which the recession and prospects for economic recovery have been the dominant theme.

But the volatile issue of the financially troubled Social Security system, which Reagan raised Thursday in a campaign swing through the West, added a last-minute spark to the campaign.

Kennedy charged yesterday that the administration "is waiting to spring a November surprise -- a secret post-election plan to slash Social Security and tarnish the golden years of the elderly."

He offered no details of such a plan.

The president countered in GOP television ads scheduled for broadcast last night in 60 regional markets that Democrats "have tried to frighten the elderly about Social Security. Well, they are wrong . . . and they know it."

The president promised, as he has before, to "protect the solvency" of Social Security and to "protect the benefits of those who depend on it." He did not say by what means.

Last week, the National Republican Congressional Committee withdrew a controversial fund-raising letter that asked GOP contributors to choose between different plans for altering Social Security. One of the options was making the system "voluntary."

Then, on the campaign trail Thursday, Reagan charged that Democrats were planning to use "demagoguery" and "falsehoods" about Social Security in the final days of the campaign.

A presidential commission is scheduled to report after the election on alternatives for shoring up the massive federal pension system, and both parties have been raising the issue gingerly, without being explicit about what changes they will support after Tuesday.

Treasury Secretary Donald T. Regan yesterday said the commission will report well in advance of its December deadline.

"We're very hopeful for getting a report in mid-November from them so that we can go to work on it, possibly with the lame-duck session of Congress," Regan said on the Cable News Network program "Newsmaker Saturday."

Kennedy's pretaped broadcast at 9 a.m. yesterday was made from the home of the Bob Spellane family in Worcester, Mass. Spellane is an assembly-line worker who lost his job last month at the General Motors plant in Framingham.

"There is an overriding issue in this election," Kennedy said. "It can be expressed very simply in a question that Reagan asked in the last campaign . . . 'Are you better off today than you were two years ago?' "

Reagan's noon address was delivered in the form of a point-by-point response to a telegram he received Oct. 12 from Sen. Donald W. Riegle Jr. (D-Mich.), who warned that Reagan's program would lead to "further collapse of the economy." Reagan did not identify Riegle in his broadcast.

The president said he found it "hard to understand" Riegle's comment about collapse and reviewed his case that the administration has made progress on problems it inherited. In response to Riegle's claim that many Americans are "searching in vain for jobs that do not exist," the president conceded this is "true" but added that jobs also are going unfilled because workers lack training for them.

Reagan again pointed to help-wanted advertising in the nation's metropolitan papers, saying there were 34 pages two Sundays ago in The Washington Post and 52 in the Los Angeles Times.

He did not mention, however, that the help-wanted index, a broad measure of employment advertising in 51 major U.S. newspapers compiled by the Conference Board, a business research organization, declined again in September to a seasonally adjusted level of 73, compared with 112 a year ago and 78 in August. The 1967 level equals 100.

Kennedy and Reagan blamed economic difficulties in part on the Federal Reserve Board's conduct of monetary policy.

Reagan noted the Fed's tight rein on the money supply last year and said it kept interest rates high into the summer, "when the recession worsened substantially."

Kennedy said Democrats "will seek reform" of the Fed to keep interest rates down, "not only in the days before an election, but throughout the years ahead."