House Appropriations Committee Chairman Rep. Hal Rogers, R-Ky. walks through a basement corridor on Capitol Hill in Washington, Wednesday, Dec. 9, 2014, on the way to a House Republican Conference meeting. With time running short before Congress adjourns, Republicans and Democrats agreed Tuesday on a $1.1 trillion spending bill to avoid a government shutdown and delay a politically-charged struggle over President Barack Obama's new immigration policy until the new year. Rogers said the measure "will allow us to fulfill our constitutional duty to responsibly fund the federal government and avoid a shutdown." (AP Photo/J. Scott Applewhite)

WASHINGTON -- Congress has been demanding an overhauled, cheaper census for the last five years, but the spending bill unveiled Tuesday night fails to pay for work needed to achieve the goal, census advocates say.

Instead, Congress may find itself having to pay billions more than it already does, or be forced to accept a significantly less accurate measure of America, which would carry its own high economic and governmental costs, according to advocates.

The census is required by the Constitution to count everyone in the nation every 10 years, an endeavor that has gotten increasingly expensive for many reasons, including population growth, inflation, rising distrust of government, and increased difficulty tracking everyone down and getting them to answer.

For the last several decennial counts, the cost has roughly doubled from one to the next. After the last one, which came in slightly cheaper than predicted at $13 billion, Congress ordered the Census Bureau to figure out how to do it cheaper.

With traditional, labor-intensive methods -- sending letters and then deploying an army of door-knockers to find people who don't answer -- the count can only get more expensive.

To try to save at least $5 billion, the agency proposed developing new technology that would use the Internet and public records to help develop what's known as a master list and match it to actual human beings. But that has not been done before. To be sure it would work, the Census Bureau began testing several new methods this year.

In order to keep that work going, the White House asked Congress for a budget of $963.4 million, a significant boost from 2014, but one to be expected at this point in the census cycle if everything is on track. However, Congress often fails to meet the need, and this year decided to short the request by some $123 million. Census defenders said that is simply not enough to do the job right.

"2020 is going to come, the census will be fielded, and if it is fielded with procedures that have not been fully tested, they will not work well," said Kenneth Prewitt, a former director of the census now a professor at Columbia University.

"The Census Bureau's funding level is extremely disappointing, essentially cutting the funding ramp-up for 2020 census planning by half," said Terri Ann Lowenthal, co-director of the Census Project, an advocacy group that includes local governments, companies, researchers and foundations that rely on the census. "2015 is a critical year for field testing that will inform the design selection for the next census. Congress wants a radically different census -- accurate but lower cost -- but it isn't willing to invest in the groundwork needed to reach that goal. I think lawmakers are putting the accuracy of the next census at grave risk."

The first problem that would stem from an inaccurate count is that federal resources would not be properly distributed to meet needs. Areas that get under-counted would end up losing federal dollars, and areas that get over-counted would get more. Typically, poorer urban areas and remote rural areas are the ones that suffer. Miscounts also often lead to expensive lawsuits.

Without properly testing and perfecting the new systems, "It’s going to end up being a less even-handed census," Prewitt said.

Businesses that rely on the government data to generate tens of billions of dollars in economic activity also take a major hit from bad data.

Congress has in the past tried to make up for lost time, but Prewitt said that just doesn't work.

"What the country has to understand, and the Congress has to understand, is that this is a relentless calendar," Prewitt said, comparing census complexity to a major military operation -- with less flexibility.

"You can delay an invasion if you’re not ready to invade. We’ve never delayed the census," he said. "And if the Congress doesn’t understand the relentlessness of this calendar, they will underfund it at a key moment."

Congress doesn't see it that way.

"The funding level for the census is sufficient to carry out necessary activities," said Jennifer Hing, a spokeswoman for the House Appropriations Committee, which negotiated the funding down from the higher level that the Senate sought.

"The periodic censuses account, which funds the decennial census, while lower than the request, received the largest percentage increase in the [Commerce, Justice and Science] portion of the bill," Hing said. She said it was an increase of $147 million, or 21 percent, from fiscal 2014.

But in recent decades, the mid-cycle bump is usually at least 30 percent, census experts said.

Prewitt said he understands why politicians, especially in today's divided Congress, aren't willing to look ahead, even four or five years.

"Congress has a habit of forgetting the census for eight years," Prewitt said. "We’ve been doing it since 1790, and thus far the instinct of Congress at about this stage has been, 'This isn't out problem. Let someone else figure it out.'"

While Congress leaves it to a future Congress to figure out, it will be the same taxpayers who foot the bill to solve any failures. "That will be money not well spent, when Congress could spend half as much now and get it right," Prewitt said.