Vice President Bush, seeking to blunt Walter F. Mondale's attacks on the Social Security issue, today told a crowd of 500 senior citizens here that Mondale plans to make "massive cuts" in Medicare benefits and blamed Congress -- not the Reagan administration -- for cutting 500,000 people off disability rolls between 1981 and 1983.

Both charges are disputed.

Mondale campaign spokesman Scott Widmeyer said that Mondale plans to save $12 billion in Medicare spending by 1989 by containing hospital costs, which he distinguished from cutting benefits.

The disability cuts, a source of controversy all year, were first mandated in a 1980 law. But Democrats say Reagan's Office of Management and Budget went far beyond Congress' intentions in the zeal with which it acted to move recipients off the rolls.

Bush was not available to answer questions about his charges because of a policy adopted this week by his campaign of restricting reporters' access to him.

Bush's press secretary, Peter Teeley, said he "absolutely" has limited Bush's availability to the national news media because "there are days when we would like to go out and make a speech and have the press report what we say," rather than focusing on Bush's responses to reporters' questions.

Today, at this retirement community south of Los Angeles, Bush said Mondale has "been demagoguing the Social Security issue up and down this country." He then said Mondale had "called for massive reductions, cuts, in Medicare, $12 billion in the year 1989."

Teeley said Bush intended to imply that the cuts would come in benefits.

Asked by an elderly man in the audience why President Reagan should be trusted, given the removal of 500,000 people from the disability rolls, Bush responded: "The thing you're talking about was imposed by the Congress and has been corrected by this administration."

However, Congress' original estimate of budget savings from the disability cuts was about $150 million, while OMB officials under Reagan at one point contemplated saving as much as $1 billion through paring the rolls. The administration placed a moratorium on the cuts after a national uproar. Reagan last week signed legislation relaxing restrictions placed on disability eligibility in 1980. He opposed the measure until after it passed the House last summer by an overwhelming margin.

"Look at the record," Bush said. "The benefits are up, and the people that go around trying to scare the American people in 1984 -- just as they did in 1982, just as they did in '80 -- about Ronald Reagan and Social Security are demagogues. They are not telling the truth. We saved the system."

Bush, who used to hold a news conference in each city he visited -- which worked out to two such sessions a day -- will now hold no more than one a day and has not answered reporters' questions since Friday.

Bush canceled a news conference today in which he was to release quotes from Mondale to substantiate his charge that the Democratic ticket had said the Marines killed in Beirut "died in shame."