DES MOINES, IOWA, JAN. 5 -- Sen. Paul Simon (D-Ill.), who has been criticized by rivals for the Democratic presidential nomination for not providing details of his plan to balance the budget within three years, said here tonight he would consider a surcharge on wealthy taxpayers "as a last resort."

It was the first time in the campaign that Simon has raised the possibility of increasing the income tax.

"If in my first year as president, when I examine the budget I inherit and find that a larger down payment will be necessary to balance the budget, as a last resort I will not duck the hard choices on the revenue side," Simon said in a speech billed by his aides as the keynote of his 1988 campaign.

"If necessary, I will ask the wealthiest of Americans, who have benefited greatly over the past seven years, to assume a greater burden," he said.

Simon said he would impose a surcharge on the top one percent of taxpayers -- individuals who earn more than $100,000 a year, or a family of four that earns more than $193,000 per year. He said that for every one percent of the surcharge, $2 billion would be raised.

He did not specify how large a surcharge he would consider, saying only that it would be at a level needed to assure $30 billion in deficit reduction in a first-year budget. He would resort to it, he said, only if other deficit reduction measures, such as a 6 percent defense budget cut and hoped-for decreases in interest payments and costs associated with high unemployment, were ineffective.