What has been hailed as one of the most innovative federal buildings in history, second only in size to the Pentagon, now has a price tag to match its excess and congressional investigators want to know why.

Why has it nearly doubled in price? Why did the development contract go to the highest bidder? And why did Washington Mayor Marion Barry have a say in who got that contract?

The building is just one more example of the twisted way in which the federal government shops for office space -- leasing when it should buy, buying when it should lease and paying more than it should in both cases.

The project is an International Culture and Trade Center in Washington, on Pennsylvania Avenue between the White House and the Capitol. The concept for the building is fuzzy -- offices for various agencies, including some that deal with trade policy, plus a performing arts center and shops. The plan is to have a private developer build the trade center and lease it to the government for 30 years, after which the taxpayers would own it.

It was inevitable that the federal government couldn't pull off a project of such magnitude -- 3.1 million square feet -- without stumbling. Construction has not yet begun and the price tag, once estimated to be $460 million, is now well over $800 million. It may hit $1 billion before Congress says enough is enough.

A presidential commission, the Pennsylvania Avenue Development Corp., made up of business people, federal bureaucrats and government officials, is overseeing the project.

Some members of Congress suspect the PADC may have violated the law in the way the development contract was awarded, and that the rising costs will turn into a major financial disaster.

"It may be the biggest white elephant the government has ever gotten itself involved in," one congressional insider told our associate Scott Sleek.

Last October, the PADC gave the contract to the Delta Partnership, a company that offered to do the job for $746 million, which was nearly $250 million higher than the lowest bidder. The PADC said simply that it liked the Delta design better than the others.

Delta is controlled by people who have developed other controversial projects in Washington, including one man who is a former consultant to the PADC.

Barry is a voting member of the PADC but rarely casts his ballot. He is normally represented at meetings by one of his underlings. But the mayor showed up at the October meeting and cast his vote for Delta. We have learned that Congress is probing the legality of Barry's vote because of a law that says federal money can be committed only by federal employees.

Before the vote, Barry wrote a letter to the PADC saying that "commitments to affirmative action" were just as important as the design of the building.

In addition to investigating Barry's role, members of Congress are also raising eyebrows over the cost. They should be tearing their hair out. Critics say the price may rise over $1 billion, more than twice the original estimate. That will drive up the rents for every federal agency that uses it.