All but 27 farmers left enough liquid assets to pay taxes owed, the budget office found, although it hinted that the actual number might be zero. The study examined how much in cash, stocks and bonds these farmers left to pay estate taxes, but the report noted that no data existed on how much life insurance the farmers had put into trusts. Virtually all wealthy farmers own life insurance in trusts, say estate tax lawyers who specialize in working with farmers.

These findings come as the Senate is poised to vote this month on repeal of the estate tax. Advocates of repeal have begun showing commercials criticizing senators who oppose repeal, like Maria Cantwell, Democrat of Washington. Many of the criticisms focus on a supposed threat to family farms.

The estate tax raised an estimated $23.4 billion last year. Repeal would shift part of the burden of taxes off the fortunes left by the richest 1 percent of Americans, some of whose fortunes were never taxed, onto the general population. The lost revenue could be made up in three ways: through higher income taxes; reduced government services; or more borrowing, which would pass the burden of current government spending to future generations.

President Bush, the American Farm Bureau Federation and the National Cattlemen's Beef Association have asserted that the estate tax is destroying family farms. None, however, have cited a case of a farm lost to estate taxes, although in June 2001 Mr. Bush said he had talked to such farmers.

The number of farms subject to the estate tax, always a minority, has fallen because Mr. Bush persuaded Congress to raise the threshold for estate taxes to $1.5 million, double that for married couples, for last year and this year. With simple planning, couples with children can shield several million more dollars from the tax.

In 2000, when the threshold was $675,000, taxes were owed by 1,659 farm estates, the study found. Had the current threshold been in effect, only 300 farms would have owed any tax.

Next year, when the threshold rises to $2 million per person, just 123 farms will be subject to the estate tax, the study found. And in 2009, when it rises to $3.5 million, only 65 of the nation's 2.2 million farms will be affected, the study said.

The study examined who would have paid estate taxes had the current exemption levels been in effect in 2000. It noted that half of all estates left by farmers had a value of less than $987,000, well under the current threshold for owing estate tax. It found that 95 percent of estates left by farmers were worth $3.2 million or less, an amount that a married couple could easily shield from tax.

The cattlemen's group, in materials distributed Friday, asserted that $125,000 of tax was owed on farm estates valued at $1 million even though estates of that amount were exempt from tax.

Jay Truitt, vice president for government affairs at the cattlemen's group, said on Friday that the Congressional study was "a fairly comprehensive piece of information." He did not dispute the estimates of the shrinking number of farms affected by the estate tax or the small number lacking enough liquid assets to pay taxes.

But, Mr. Truitt said, the study did not examine the effect of using liquid assets to pay estate taxes. When such liquid assets are diminished, he said, a cattle operation is starved for capital and can "go years not making a profit," which means fewer jobs.

Neil E. Harl, an economics professor at Iowa State University whose expertise in estate tax planning for farmers has made him a household name in the grain belt, said many Americans had a false impression that the estate tax was destroying family farming.

He said the Congressional study "adds to the weight of the evidence that this is a myth that has been well spun."

"Farms, in particular," Mr. Harl said, "are not in jeopardy because of estate taxes."

Michael J. Graetz, a professor at Yale Law School who was a tax policy official in the administration of President George Bush, said repeal was primarily a benefit to people with large estates held in stocks and other securities, not to farmers.

Professor Graetz is a co-author of "Death by a Thousand Cuts," a study of how estate tax repeal became a political issue. He said that rather than repeal the tax, Congress should raise the threshold to as much as $5 million, double that for married couples, and keep rates at or near current levels.

Because of details in the repeal bill, it would also force a large majority of farms and small businesses to pay larger tax bills in the future, said John Buckley, the chief tax lawyer for Democrats on the House Ways and Means Committee. Mr. Buckley criticized farm and small-business groups as not explaining to their members that the repeal as written would cost them money while primarily benefiting those with vast fortunes.