Washington ? Most taxpayers could expect a rebate of up to $600 starting in mid-May under the economic aid plan set to go through Congress within weeks.

Couples could get twice as much, with even more for most families with children. All that, however, depends on smooth sailing at the Internal Revenue Service, and the agency already is up to its eyeballs in filings and refunds.

The Treasury Department says that despite the strains of tax filing season, the IRS will be able to begin delivering the payments within 60 days after President Bush signs the plan into law, and complete the process in approximately 10 weeks, possibly sooner. The payments would come separately from regular tax refunds.

But figuring out if you qualify – and for how much – can be complicated, thanks to confusing rules designed to get the money to middle-income workers and ensure it also benefits low-income people who are most likely to spend the cash.

“Almost everyone who earns income will receive some benefit,” said Douglas W. Elmendorf, an analyst at the Brookings Institution. “The idea is to target the money on the people who will spend a large share of it, and to target it on people who are likely to be hurt by an economic downturn.”

About three-quarters of those eligible for the checks are working people. About one-quarter would qualify solely through pension or interest income, such as retirees or people who are unemployed. Eligible people would get at least $300.