WASHINGTON — More than 40,000 estates worth $1 million to $10 million would be expected to escape inheritance taxes next year under the deal struck by Republicans and President Barack Obama.

The package would leave only about 3,500 of the largest estates subject to federal taxes next year, a boon for the wealthy that many House Democrats say they can’t accept.

The estate tax has emerged as one of the biggest obstacles to bringing Democrats aboard the tax cuts-employment benefits package negotiated by Obama and GOP leaders in Congress. House Speaker Nancy Pelosi called the lower estate tax “a bridge too far.”

The federal estate tax reaches fewer than 1 percent of inheritances, but it has long been a political lightening rod among lawmakers from both parties. Many Republicans want to eliminate the estate tax altogether, derisively calling it a “death tax” that makes it hard for parents to transfer small businesses to their children.

Estate tax opponents got their wish this year, when the tax was temporarily repealed. But the tax holiday will be short-lived because, under current law, the estate tax is scheduled to return next year with a top rate of 55 percent for estates larger than $1 million for individuals and $2 million for married couples. The package Obama negotiated would set the top rate at 35 percent and exempt the first $5 million of an individual’s estate. Couples could exempt $10 million.

At those levels, the tax would affect just 0.14 percent of all estates in 2011, or about 3,500 estates, generating about $11.2 billion in revenue, according to an analysis by the Tax Policy Center, a Washington research group.