The astronomical costs of building the Second Avenue subway and other New York public transit projects are now the subject of a federal inquiry.

The Government Accountability Office said on Wednesday that it was preparing to launch a study of why transit construction is so much more expensive in the United States than in other parts of the world. Special attention is expected to be paid to New York City, where recent projects have cost far more than anticipated.

Auditors plan to examine contracting policies, station design, project routing, regulatory barriers and other elements that drive cost, comparing practices in different cities in the United States and abroad, officials said. A final report with recommendations is to be issued by the end of the year.

The study was part of the spending bill that was approved by Congress last week. And it comes three months after an investigation by The New York Times revealed how city and state public officials had stood by as a small group of politically connected labor unions, construction companies and consulting firms drove up transit construction costs and amassed large profits.