President Reagan and Walter F. Mondale both made some exaggerations and misstatements in last night's debate.

In their jousting over Social Security, Reagan disputed Mondale's assertion that he had proposed cutting the benefit program by 25 percent. Reagan responded that "the only 25 percent cut that I know of" came in 1977, when the Carter administration raised Social Security payroll taxes and the wage base on which those taxes are levied.

The Reagan administration did propose in 1981 to cut Social Security benefits by $82 billion over five years. In 1982, Reagan proposed cuts of $40 billion over three years. The 1981 cutback would have reduced benefits by nearly 25 percent from the level that future retirees would receive under current law.

President Carter's 1977 tax increase, on the other hand, included no significant benefits reductions. Reagan apparently was suggesting that future recipients would lose ground by having to pay higher Social Security taxes.

When asked about his dedication of a subsidized housing project for elderly and handicapped residents in Buffalo, Reagan said that "our policy was not to cut subsidies" in housing.

But the administration did propose cutting the "Section 202" housing program for the elderly and handicapped from more than 16,000 units in 1981 to 10,000 units this year, although Congress made smaller cuts.

Mondale overstated his criticism, however, in saying that "the president's budget sought to terminate" the program and that if Reagan had had his way, the Buffalo project never would have been built. But Mondale was correct in saying that Reagan has made massive cuts in subsidized housing for the poor.

Reagan said he expected to cut the federal budget deficit, without raising taxes, to between $30 billion and $40 billion by 1989. When questioner James Wieghart noted that the nonpartisan Congressional Budget Office had estimated that current policies will produce a $263 billion deficit by 1989, Reagan responded that he did not believe the CBO.

The president said there are "more people receiving food stamps than were ever receiving them before," even though some less-needy recipients have been dropped from the rolls.

Agriculture Department figures, however, show that since Reagan took office the number of food stamp recipients has dropped from 20.7 million to 20.3 million.

Reagan also said that while the poverty rate had increased during his term, "it is a lower rate of increase than it was in the preceding years, before we got here." Although Reagan did not specify the period he had in mind, Census Bureau figures show that during Carter's term, an average of 1.1 million people a year fell into poverty, and since Reagan took office an average of 2 million a year have dropped below the poverty line.

Mondale reopened a long-running debate about whether the president's three-year tax cut had unduly benefited the rich. Reagan contended that the rich had not received a disproportionate share of the tax cut in terms of percentage as opposed to dollars.

Comparisons are difficult because of deductions and other factors, but a study by the nonpartisan Urban Institute found that the tax cut reduced the share of family income nationally for the poorest fifth of the population by .7 percent, while increasing it for the most affluent fifth by 1.9 percent.