A letter came last month to Rep. Mary Rose Oakar (D-Ohio). In the heap of daily mail that every congressional office must contend with, this one differed. It was personal. The writer was a classmate of the congresswoman at Ursuline College in Cleveland, from which both had graduated. The two women had kept in touch over the years, the one going into politics, the other to marrying and children.

This was another keeping-in-touch letter, except that as Oakar read into it, she felt her stomach tightening. "I'm really desperate at this point," the letter began. "Bob still hasn't found a job and we can't even begin to pay the bills. He's totally demoralized. As a matter of fact, we've applied for food stamps. With Christmas coming, and five children, it's really a nightmare. It's been said that hardship brings people closer. However, the stress has really had an effect on our entire family. We've exhausted our supply of money, have cashed in our life insurance dividends and the next step is a second mortgage on our house. We've reached a point of no return. . . ."

Oakar didn't doubt it. She said that for her friend to write this way was a humiliation. The congresswoman made the letter public at hearings in December, when the House was considering a committee-passed proposal to provide $50 million in emergency funds for the homeless. The sum, compared with the need, was so small as almost to be a token. Congress, having taken care of itself with a pay raise, denied the pittance anyway.

As read by Oakar, the letter represented word from a new group of Americans, the potential poor. Nineteen- eighty-two saw the emergence of what the press is calling the new poor. Their visibility created a year-long story that couldn't be ignored. Cheese lines offered startling visuals for television news camera crews. Reporters went to the unemployment offices for interviews with people who gave reality to the worsening umemployment figures.

The potential poor will be harder to find than the new poor. They still have homes, cars and food. Like Oakar's friend, they are educated and live in clean neighborhoods. But one more rub against the unexpected will mean a forced drop into poverty. They would have gone voluntarily by now, except that the secret challenge of their suddenly desperate lives is to resist the public humiliation of the welfare line.

Many of the potential poor are citizens who voted for Ronald Reagan. They were not offended, and perhaps even said right on, when David Stockman expounded his philosophy of government:"I don't think people are entitled to services. I don't believe there is any entitlement and basic right to legal services or any other kind of services."

That early attitude has prevailed even as the visibility of the nation's poverty sharpens into new starkness. As recently as last week, reports stated that Stockman's Office of Management and Budget has plans to cut $1.4 billion more in such programs as food stamps and school breakfasts for poor children. More people are hungrier--and this administration responds by taking away food.

Even to the penny, when kids are involved. The OMB proposal, according to a news report, would cut an extra allotment that children from poor neighborhoods receive for their school meals. The allotment per meal? Two cents. The policies are one insult. The official cynicism behind them is the other.

Reagan, commenting on the reports of what his decisions were doing to people, said last year: "Now you're hearing all kinds of horror stories about the people that are going to be thrown out in the snow to hunger and die of cold and so forth. . . . We haven't cut a single budget. . . . We have been reducing the rate of increase that has been built in and that has been submitted to us for consideration in these budgets."

That was a year ago at budget time. After the reductions, he persisted: "There have been no budget cuts. . . ." Since then, mockery has been added to the cynicism. The entitlements denied to the poor are being taken at the other end--by rogue officials at programs like Legal Services and HUD who are milking the government for dubious travel expenses.

This is about the time Ronald Reagan should be showing signs of growing in office. At two years, the evidence suggests shrinkage. In the homes of the potential poor, like Oakar's college friend, no help from the top is seen. All that's visible is the fall at the bottom, unbroken by government concern.