In negotiating the budget deal that averted a government shutdown, Democrats and the White House claimed a big victory in preventing Republicans from blocking a set of environmental regulations. But as details of the compromise became known Tuesday, it was clear Republicans had won deep reductions in spending at the Environmental Protection Agency.

Under the deal headed to House and Senate votes by the end of this week, the EPA's 2011 budget would be reduced by 16% from 2010 spending, taking it to $8.7 billion.

That...