Washington ? Millions of economic stimulus payments sent after-tax incomes surging in May by the largest amount since a similar recession-fighting effort by Gerald Ford 33 years ago.

All the extra money helped to push consumer spending up by the biggest amount in six months, but economists warned the boost would likely prove short-lived given all the other problems now facing consumers.

The Commerce Department reported Friday that after-tax disposable incomes jumped by 5.7 percent in May, the biggest one-month gain since a 6.3 percent increase in May 1975 when Ford was president. He was fighting a recession that year with a program to mail individual taxpayers $50 checks.

This time around, individual payments range from $300 to $600 with couples getting up to $1,200. In all, $48.1 billion in rebate payments were made in May. Through the end of this week, the government announced Friday, payments now total $78.3 billion, which is three-fourths of the $106.7 billion scheduled to be paid to 130 million households. The payments are to be completed by mid-July.

Bolstered by the big 5.7 percent surge in after-tax incomes, consumer spending rose by 0.8 percent last month, the best showing since November. Even after removing the effects of higher gasoline and other products, inflation-adjusted spending rose by a solid 0.4 percent, the best performance since last August.

Since consumer spending accounts for two-thirds of total economic activity, analysts said the big jump in May should guarantee a positive reading for overall economic output in the current April-June quarter of around 1.25 percent to 1.5 percent, up from 1 percent growth in the January-March quarter.

Growth at that level is also expected in the third quarter, but analysts said the fourth quarter of this year and first quarter of next year could well sag and even turn negative as the effects of the stimulus payments wear off.

“The stimulus payments are likely to be a temporary boost and come the fall, consumers will be wondering how they are going to pay their bills with gasoline at $4-plus, unemployment rising and housing values and stock prices falling,” said Mark Zandi, chief economist at Moody’s Economy.com.