Interior Secretary Ken Salazar said Thursday that his department would allow Royal Dutch Shell to start “certain limited preparatory activities” for oil drilling in the environmentally sensitive waters off Alaska’s northwest coast.

Salazar said Shell can now construct what is known as a mud line cellar, a 40-foot-deep structure needed to install a blowout preventer, a device that can help head off spills. He said Shell would also be allowed to drill two 1,400-foot holes that would be used for additional sensing equipment.

“Today’s action does not authorize Shell to drill into oil-bearing reservoirs,” Salazar said.

The partial go-ahead was given to Shell because time is running out on the open-water season before the ice returns and prevents drilling. Shell is scrambling to drill one or two wells, though it had initially hoped to complete five or six in the Chukchi and Beaufort seas this year.

Before it drills into oil-bearing reservoirs, the company will have to ready a spill containment vessel that must be certified.

Salazar said that Shell estimates that its containment vessel could be certified in four or five days, and it will take several more to move the vessel to the drilling area 70 miles off the coastal Inuit town of Wainwright.

That doesn’t leave much time. The Interior Department has said that Shell would not be allowed to drill in the Chukchi Sea past Sept. 24, early enough to leave time for a relief well to be drilled in the event of a spill. The deadline is Oct. 31 in the Beaufort Sea.

The company’s drilling program has been delayed by an unusually cold winter that left more multi-year ice in place as well as its inability to obtain a permit for a 4,700-ton oil-spill-containment system that Interior’s Bureau of Safety and Environmental Enforcement requires.

The company’s exploration plans have drawn protests from environmental groups worried about a possible spill in an area that is icy and dark much of the year and is home to seals, walruses and whales. The BP oil spill in the Gulf of Mexico in 2010 heightened anxieties over spills.

“The Department of Interior should not be bending over backward to accommodate a company that simply cannot get its act together,” said Michael LeVine, Pacific legal counsel at Oceana, a conservation group opposed to offshore drilling. “The window is closing and the company doesn’t have anyone to blame but itself.”

Shell has spent seven years and more than $4 billion buying leases and preparing for exploration in the Chukchi Sea. The Obama administration, despite environmental concerns, has supported Shell’s exploration program, but it has required Shell to comply with stiff guidelines for safe drilling and spill response.

“We appreciate the effort the Department of Interior has made to understand, scrutinize and support this project of national significance,” Shell said in a statement.