SOUND AS the proposal might be as an idea, it could not easily be defended against attacks of this sort. The proposal "can't be defended in three minutes or indeed three months," Mankiewicz said. "For a minute of ridicule, you need an hour of serious undivided attention to answer some of the wilder criticisms."

"If you're President, maybe in two years you can make some headway," he said. But if you're presenting the proposal in a campaign, you are unlikely to obtain the public understanding necessary to get such a proposal across."

Yet, as Mankiewicz noted himself, there are politicians who can handle complicated proposals in debate. When critics attack Senator Edward M. Kennedy's health insurance plan, for instance, "they're the ones who look like they don't know what they're talking about," he said. Kennedy "knows that plan, he's been living with it for a long time, and he can defend it quickly and competently with critics." Clearly, McGovern knew his own plan less well.

Humphrey "went after McGovern in a far tougher way than would ordinarily be his style...[and] McGovern was surprised," commented Ted Van Dyk, who advised Humphrey on issues in 1968 and did the same for McGovern after the 1972 convention. "Were we in the same position as Humphrey, had it been our last chance, we probably would have attacked his record on Vietnam," he said.

For a front-runner, however, it didn't make good sense to "get too tough with the opposition candidate" in the party. It might endanger the election. A good party man, an old liberal like Humphrey, would probably have preferred not to attack a fellow Democrat either, especially on liberal issues. But, because of his political situation, he did. And, in so doing, he made Nixon's job a lot easier. Nixon didn't have to say much about McGovern on the issues. Humphrey had already said quite a bit.

Humphrey had subjected McGovern to the kinds of attacks he would have to expect when he went before voters of both parties. McGovern's strong liberal stand on the issues was no longer the asset it had been in the early primaries. Now he was on the defensive.

Mankiewicz and others in the campaign felt Humphrey's attacks on the welfare proposal were "political" and "dishonest." And indeed they were. But these are the kinds of attacks that liberal reform proposals will inevitably receive. A liberal "issues" candidate must be prepared to defend himself against criticisms of this sort. And McGovern wasn't.

AFTER THE California primary, a great deal of work was done on McGovern's welfare proposal, though in a sense, it was already too late. The proposal was permanently stained. From mid-June on, a task force of economists made an intensive computer study--the kind that should have been made before McGovern made a specific proposal--of a large variety of plans based on the "demogrant" or annual payment principle. But by early August, it was clear that the demogrant could not be made to fly; it was too expensive and raised too many technical questions which could not be satisfactorily resolved or explained in the campaign.

Politically, one of the plan's most nettlesome problems was that it would require making major changes in the present tax system. Indeed, as Tobin had pointed out in his articles, this was one of the purposes of the plan. But as he had also pointed out, this was not an easy idea to sell.

Besides replacing the existing tax structure and substituting tax credits for exemptions, the plan would require a wholesale elimination of deductions and exclusions. This would be necessary to bring in more revenue from high income taxpayers and to ensure that net benefits at lower levels were based on a realistic reflection of recipients' real income. (The idea behind the whole scheme was to simplify the tax structure so that taxpayers--the rich in particular--could not hide behind the tax shelters the present system provides.)

After the demogrant was dropped, attention was focused on a cheaper plan which left the positive tax system intact. Under this plan, a family of four with zero income would still receive $4000 but its net benefits would cease at $8000. Above that income, it would stop receiving benefits altogether and would enter the regular tax system.

The plan, a standard negative income tax, provided a weaker work incentive than the demogrant, since it would reduce benefits faster as income rose. And it would do much less for the middle class. To some economists, who were concerned about poverty but less with redistribution per se, this was a positive advantage of the new plan. Heather Ross, the economist who had prepared it, took this view.

She opposed the demogrant because "it gives money to people who don't need it." She objected to "giving so much to blue collar workers for new cars and television sets, when so much is needed in the public sector."

She doubted, also, whether "there's any political mileage in making those people net beneficiaries. You could give them a lower net tax payment. But once you go over to positive payments, you lose all the excitement of that proposal," she said.

This is a critical point. McGovern thought the demogrant would create allies in the middle class, aides said, especially on the issue of welfare reform. But he probably misjudged the public mind. Middle class Americans may be angry that they are losing so much of what they earn through taxes. And they may think that the rich are not paying their fair share. But they do not expect the rich to give them money. They believe that they--and the poor--deserve only what they earn through work.