President Reagan yesterday reclaimed the offensive on Social security, accusing the Democrats of "opportunistic political maneuvering" on the issue and saying he will ask for time on nationwide television to rally support for a "bipartisan" solution to the system's financial problems.

Reagan made only oblique reference to the Democrats' latest jab at his proposed Social Security cutbacks: a resolution calling for retention of the $122-a-month minimum Social Security benefit for current recipients. Both houses, at Reagan's request, earlier voted to eliminate the benefit as part of the omnibus package of spending cuts.

The resolution is scheduled for a House vote today, just as the National Council of Senior Citizens stages a mass rally on the steps of the Capitol to protest Reagan's Social Security proposals.

Republicans in both houses have acknowledged that the political fallout from proposed Social Security cuts is mounting, and House Republicans late yesterday were working on a strategy to head off or neutralize the Democrat's resolution, including the possiblity of a counter-proposal to protect the neediest of the 3 million recipients of minimum benefits.

In his letters to Republican and Democratic leaders of both houses, Reagan also sought to neutralize the issue by serving notice that he will go before the country "as soon as possible" to "call on the Congress to lay aside partisan politics and join me in a constructive effort to put Social Security on a permanently sound financial basis."

But Reagan got in some partisan licks, too, saying he deplored "the opportunistic political maneuvering, cynically designed to play on the fears of many Americans, that some in the Congress are initiating at this time."

"These efforts appear designed to exploit an issue rather than find a solution to the urgent Social Security problem," Reagan said. "They would also have the unfortunate effect of disrupting the budget conference and reversing the actions of a majority of both houses of the Congress. Such a result would jeopardize our economic recovery program so vital to the well-being of the nation."

Reagan's reference to the budget conference stemmed from a proposal by House Majority Leader James C. Wright (D-Tex.), author of the Democractic resolution, that House conferees on the spending cuts legislation be instructed to keep the minimum benefit, even though both houses have voted to eliminate it. However, the resolution makes no reference to the conference, and democratic budget leaders have said they favor separate legislation to reinstate the benefit.

Far from silencing his Democratic critics, Reagan prompted an in-kind response from House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), who attacked both elimination of the minimum benefit and Reagan's more far-reaching proposals to cut future benefits.

"The old age and disability benefit cuts proposed by your administration are twice as deep as necessary to keep the system solvent," O'Neill said. "They are ill-advised and unacceptable. It is unconscionable to create and exploit fears about the fate of the Social Security system so as to make deep cuts in benefit levels."

The Democratic National Committee also made clear it didn't think the president was rising above politics. The committee called major television networks to say the Democrats want time to respond if Reagan gets time for an address on Social Security. White House officials said a specific time will not be requested until after Reagan returns from talks in Ottawa.

Meanwhile, Sen. Donald W. Riegle Jr. (D-Mich.) yesterday introduced an amendment to the tax cut bill to retain the minimum benefit for those who receive or qualify for it this year. It will be voted on today. A previous Reigle effort to retain the benefit failed earlier this month, 53 to 45.

In conferences to resolve differences in the nearly $40 billion worth of spending cuts approved earlier by both houses, banking committee conferees agreed to retain Urban Development Action Grants as a separate program, against Reagan's wishes. They also approved tighter restrictions than House Republicans wanted on small cities' block grants for health services emerged as a stumbling block in another conference.

Education committee conferees agreed to $475 million for impact aid for school districts with large numbers of federal employees; the Senate had proposed $500 million, the House about $400 million. The program now costs about $800 million. The conferees also agreed to split the difference on scaled-back funds to educate poor children.