President Reagan stepped into political quicksand more than a year ago when he proposed massive changes in the social security system. Democrats responded with shock and dismay and began churning out speeches and bumper stickers touting ''Save social security - vote Democrat.''
But with congressional elections less than two weeks away, the economy has now overshadowed the social security issue. President Reagan has pulled back on social security and put it on the back burner by setting up a bipartisan study commission, and Democrats are talking more about double-digit unemployment.
But in some areas of the country, social security is still on center stage. And nowhere more than along the booming Gulf Coast of Florida, where the influx of retirees has helped earn the state four new seats in Congress this year.
Here among the palm trees, retirement homes, and shopping malls is the new Florida Ninth District, perhaps the ''oldest'' area in the country. The suburban Tampa and Clearwater-based district has a population that is about 60 percent elderly. Close to half the residents receive social security benefits, and many rely almost solely on government checks for their livelihood.
When the new Florida district was drawn, it looked custom-made for a Republican. But that was before George Sheldon, a Democratic state legislator and Tampa attorney, seized on the social security issue.
Soon after the district lines were drawn, he began to develop the theme. ''The politicians in Washington cut $400 out of your medicare benefits. George Sheldon says that's immoral!'' blares the headline in a Sheldon campaign tabloid , sprinkled with photographs of senior citizens hugging or being hugged by candidate Sheldon. Another campaign newspaper says 10,000 senior citizens have signed the Sheldon resolution ''to protect social security and medicare.''
Republican opponent Michael Bilirakis, a Tarpon Springs attorney and former judge making his first try for elected office, complains that Mr. Sheldon has indulged in ''fear-mongering'' on social security. But he concedes, ''It has worked up to now.''
Like other Republicans in Florida, Mr. Bilirakis takes a strong stand for social security, promising to fight ''any effort to reduce or eliminate retirement and medicare benefits for current retirees or those nearing retirement.''
In fact, the two candidates are not very far apart on the substance of the issue. Even the Democrat concedes that he could accept some reforms in the system.
However, Republican Bilirakis is battling a perception that his party is weak on social security. ''The administration is facing up to the problem'' of financing social security, he argues. ''They don't have their head in the sand. The bipartisan commission (expected to issue a report in December on social security reform) is a tremendous first step.''
Trying to shift the debate to new subjects, the Bilirakis campaign has spotlighted crime, a big concern to Floridians, and Sheldon's liberal image. ''The major issue is the philosophies of the candidates,'' says Bilirakis, who has made waves by proposing that women who have abortions should be jailed and that the United Nations headquarters should move to Switzerland.
Sheldon points to his record of fighting for consumer causes, such as deregulating the truck and bus industries. He discounts charges that he has ''demagogued'' the social security issue.
''The bottom line is that I didn't propose $80 billion cuts in social security and then back off,'' he says of President Reagan's 1981 proposal to make reductions in benefits. ''I didn't cut off minimum benefits (for social security). I would not have supported $13 billion in reductions in medicare (recently passed by Congress).''
Arguing that he is not ''scaring the elderly,'' Sheldon says, ''It's David Stockman (director of the US Office of Management and Budget) that's scaring the elderly. It would be morally wrong not to point that out.''
If the Democrat wins this close race in Florida, it will probably be because he has played the social security issue correctly. In California, meanwhile, Pete Wilson, the Republican mayor of San Diego who is running for US Senate, appears to have committed a political faux pas by proposing that younger workers be given ''greater freedom'' to invest in private pension programs rather than in the social security system. His Democratic opponent, Gov. Edmund G. Brown Jr., fired back that Wilson would cut social security.
Throughout the nation, it is unlikely that many races will be won or lost on the social security issue, since the President effectively set the matter aside with the social security study commission.
However, this week the news broke that the social security pension fund has run short of money and must borrow temporarily from other funds in the system. Although the interfund borrowing had been expected, it reminds voters once again of the program's woes. And when they go to the poll Nov. 2, the Democrats are hoping those concerns will translate into votes.