The asbestos trust fund bill is back for consideration in the U.S. Senate after a hiatus during which U.S. Sen. Arlen Specter, R-Pa., urged supportive lobbyists to spend more on public relations to bolster flagging support. That time would’ve been better spent shoring up the bill’s weaknesses.

The idea of a trust fund financed by companies that have profited from the use of asbestos is sound. But the details are everything in setting up a fair system to compensate victims of asbestosis, mesothelioma and other deadly respiratory diseases.

Congressional leaders want to end asbestos litigation, which is overwhelming the legal system and prolonging economic uncertainty for many businesses. Instead, a fund would be established to more efficiently and effectively compensate victims.

About 300,000 victims are awaiting compensation. In the past 30 years, $70 billion in claims has been paid out, which has led to the bankruptcy of nearly 80 companies. A Rand study shows that 42 cents on the dollar goes to victims. Plus, the legal system does a poor job of identifying the neediest victims and weeding out illegitimate claims.

The Senate bill would establish a $140 billion trust that would be administered by the U.S. Department of Labor. Those seeking compensation would have to meet certain medical guidelines.

But there is no hard science behind the $140 billion figure. The American Legislative Exchange Council, an association of conservative state lawmakers, says the bill would establish $300 billion in entitlements. A Rand study suggests that more than $200 billion might be needed. A Congressional Budget Office study also casts doubt on whether the trust fund would have enough money.

The $140 billion figure isn’t based on what victims will need; it’s based on what industry and insurers are willing to pay.

In addition, the American Medical Association says the medical criteria are too stringent and could lock out thousands of people with significant illnesses.

Some small and medium businesses note that the funding formula would require them to pay sums that exceed their current and expected liabilities. For instance, USG Corp., the world’s largest wallboard maker, faces $3.95 billion in asbestos liabilities, but if the bill passes, that amount would drop to $900 million. The difference would be shouldered by smaller businesses.

Another significant sticking point is the exception the bill carves out for victims in the vicinity of Libby, Mont., where hundreds of people have died because of exposure to asbestos-laden vermiculite, which was mined in nearby hills. Victims there need only establish that they lived within a 20-mile radius for 12 consecutive months. Medical criteria for them are also more lenient.

Nobody begrudges compensation for those victims, but they weren’t the only ones exposed to the vermiculite that came from Libby’s mines. Millions of tons of vermiculite were shipped to processing plants in 39 states, including an expansion plant in Spokane that operated on North Maple Street from 1951 to 1973. Many of those workers would not be covered by the trust fund. Plus, victims that may emerge from the 9/11 terrorist attacks and Hurricane Katrina would be shut out.

The Senate bill doesn’t need better salesmanship; it needs better craftsmanship.