As Congress gets close this week to passing a bill that would create a first-if-its-kind database of federal expenditures, advocacy groups that have lobbied for the measure are salivating at the prospect of bolstering their own agendas with the new numbers.

But even though government watchdog groups and a cross-section of liberal and conservative organizations from Greenpeace to the conservative Eagle Forum are unified in favor of the database legislation, the unity likely will end if that information becomes public, as outside groups compete over splashy scoops and attack opposing organizations and causes.

“From left to right we are united in the notion that we should have access to the information,” said Andrew Moylan, government affairs manager for the National Taxpayers Union, which has helped spearhead lobbying for the bill. “Once we get the information, I think we all have very different ideas on how it should be used.”

Under the legislation sponsored by Sens. Tom Coburn (R-Okla.) and Barack Obama (D-Ill.), the Office of Management and Budget would set up a database of all government contracts, grants and earmarks. One estimate by the Congressional Budget Office said the database could cost up to $15 million to build and maintain.

Massie Ritsch, communications director at the Center for Responsive Politics, said his group wants to merge the federal spending database with the group’s existing information on lobbying and political campaign spending.

“When combined with our own data on contributions and lobbying, this will make clear to the public what is really spent to influence the government is a tiny investment compared to what they receive,” Ritsch said.

Another budget group, Taxpayers for Common Sense, wants to leverage the government data to provide the public with more information on spending, said the group’s Steve Ellis.

“This could be the single greatest tool for transparency in government” since the Congressional Web site THOMAS was created, Ellis said. “We’re going to have lists of these data that people can look at, review and start understanding.”

Others, however, are not as convinced.

Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington, D.C., said she’s “hugely skeptical” that the bill will come to fruition. But, she said, “I think it’s a good idea. There would be a lot of people looking at that.”

And even before the legislation has passed, some of the groups are questioning whether the database itself will be a wise use of taxpayer funds. They question the estimate that the database would cost $15 million to create and maintain over five years.

Ellen Miller, executive director of the Sunlight Foundation, said her organization awarded the nonprofit group OMB Watch a grant for $235,000 to create a similar database and maintain it for three years. That database is set to launch in early October.

“It is going to be a model for this federal database,” Miller said. “It is a remarkable instrument.” Miller said she has questioned the $15 million price tag. “Somebody needs to explain that number,” she said.

Ritsch of the Center for Responsive Politics put it more bluntly: “It makes us wonder whether the $15 million is just another overstuffed government contract that this database would be set up to track.”

But Ellis of Taxpayers for Common Sense said he sees the government expense for the database as an investment in savings.

Coburn spokesman John Hart said his boss saw it as a valuable tool and wasn’t concerned with the price of administering the database. “This fills in a very important part of the puzzle,” Hart said.

Lobbyists who focus on the appropriations and government contracting sector said they were skeptical of Coburn’s and Obama’s motivations.

“It’s just another tool for them to criticize and attack programs they don’t understand,” said one lobbyist. “This is not about solving a problem, it’s about scoring political points.”