Mr. Obama opposes extending President Bush’s tax cuts. Instead, he proposes various tax breaks, including a $500 tax credit for each person in a household who works, a larger child care tax credit, a $4,000 tax credit each year for the first two years of college, and eliminating all income taxes for those over 65 with income less than $50,000 a year.

To reduce the deficit and inequality, he would raise the tax rate for single households with incomes of $200,000 or more and for families with incomes over $250,000. He would also raise taxes on capital gains and dividends.

The median household income nationwide is $50,233, according to the Census Bureau. The Tax Policy Center found that, for married couples with incomes of $50,000, two children and both parents working, income taxes would be cut by $284 more under Mr. Obama’s plan  by $1,005, compared with $721 under Mr. McCain’s plan.

Deloitte also examined such a couple and found similar benefits; a $700 cut under Mr. McCain’s plan and $1,000 under Mr. Obama’s.

For married couples with incomes of $500,000 with two children and both parents working, the Tax Policy Center found that Mr. Obama would raise income taxes by $3,363, from $110,955 now, while Mr. McCain’s plans would leave taxes unchanged. Deloitte found that a $500,000-a-year couple would pay $3,100 more under Mr. Obama, with no change under Mr. McCain.

Clint Stretch, Deloitte’s managing principal of tax policy, said most families would benefit under Mr. McCain’s plan because of an increased exemption for each child. That, he said, would reduce taxes for low-income families by about $230 per child and for high-income families by about $800.

To help low-income families in particular, Mr. Obama would give a “Making Work Pay Credit” equal to 6.2 percent of a worker’s first $8,100 in wages. That would yield a tax credit of $500 for a single person, and $1,000 for a couple in which both adults work. As a result, a low-income couple now paying no income taxes might receive a $1,000 refund.