WASHINGTON — Forget about parties, resolutions or watching the ball drop. To Iberdrola Renewables, New Year’s Eve will mean checking on last-minute details like the data connections between 169 new wind turbines in New Hampshire, Massachusetts and California and its control center in Portland, Ore.

All over the country, developers are in a sprint to get new wind farms up and running before Tuesday, when two subsidies will disappear like Cinderella’s ball gown. After that, the nation’s wind-farm building will be at a virtual standstill.

The stakes of meeting the deadline are enormous. Wind turbines that are connected to the grid and in commercial service before midnight on New Year’s Eve are entitled to a 2.2 cent tax credit for each kilowatt-hour they generate in their first 10 years, which comes out to about $1 million for a big turbine. Or companies can request a lump-sum payment equal to 30 percent of the construction cost.

As it stands now, those that enter service on Jan. 1 or later are out of luck.

The deadline is a bit like the April 15 one for filing income taxes, but “there are no extensions here,” said Paul Copleman, a spokesman for Iberdrola. To reduce the risk of missing it — a risk that increases when managing construction projects on mountaintops in New England in the winter — the company allowed more than a year for what are normally nine-month construction projects.