Should a retiree with an income of $125,000 be entitled to the same low premium for public medical insurance as an elderly person whose income is one-fifth as much?

Should farm subsidies go to people with non-farm incomes of more than $125,000?Should school-lunch and student-loan subsidies be sensitive to means?

These questions need to be addressed by Congress as it starts considering the proposed new budget that President Bush recently submitted for fiscal 1992.

These particular queries are more urgent than they used to be because the new budget calls for adjustments in Medicare, farm programs, school lunches and student loans that would start whittling down on subsidies for the well-to-do and start redirecting aid according to need.

Yes, the proposed changes are only marginal and would bring only small increases in revenue - $1.2 billion over five years from increased Medicare premiums, for example. But at least the White House is raising an issue that ought to get increasing public attention and debate.

If Congress doesn't start coming to grips with the problem now, it's bound to become worse later. Some 41 percent of next year's budget will consist of direct benefit payments to individuals - more than double the Pentagon's 20 percent. Moreover, these mandatory outlays are programmed to keep growing.

Scripps Howard News Service quotes Richard Brandon, a professor at the University of Washington's Graduate School of Public Affairs and a former staff director for the U.S. Senate Budget Committee, as calculating that a 50 percent increase in the overall tax burden would be needed to finance retirement benefits for the baby boomers if spending continues on its present path. His figures also show that most of those retirees will be well off.

Specifically, Brandon found that by 2020 about 64 percent of Social Security and Medicare benefits will go to households whose income is more than 50 percent above a "generous middle-income standard of income adequacy."

There is no simple way of moving from the present universal entitlements to a means-sensitive system - at least none that avoids obvious pitfalls like discouraging saving for retirement. Every worker who pays into Social Security should receive benefits.

But the subject's complexity is just another argument for getting the discussion under way fast.