BILLINGS, Mont. — State officials have withdrawn their request for federal regulators to approve air-quality rules that let the oil and gas industry drill first and attain emission approvals later.

Adopted in 2005 and 2006, the rules have drawn criticism for giving companies 60 days after drilling to register with the state, with no emissions permit required.

Montana Department of Environmental Quality Director Richard Opper said Tuesday the state wants to retain the rules but needs time to rework its request to the EPA. The rules will remain in place in the interim, he said.

"We really like that program," Opper said. "Permitting every well would be very inefficient for us. This saves time, it protects the environment — it works."

More than 900 oil and gas facilities, many with multiple wells, have been registered under the program.

The withdrawal of Montana's request for approval comes after the Environmental Protection Agency said in January it planned to reject the state's rules because they violate the Clean Air Act.

A final decision from the agency was due this week, but Gov. Brian Schweitzer withdrew the request in a letter Monday to EPA regional director Jim Martin.

Montana's rules were meant to streamline energy development in the state by eliminating the need for companies to carry out emissions studies before drilling holes during exploration activities that might never be used if they turn out to be dry.

But environmentalists from WildEarth Guardians contended the rules are too risky because emissions reviews come after the fact. The group sued the EPA to force it to act on the matter after the rules languished at the federal agency for several years without a decision.

Federal law gives the EPA authority to enforce emissions limits on its own if it chooses. But officials said last month that the agency wants to work with Montana to improve its rule.

The state wants to keep the rules in part because officials said they lack sufficient resources to regulate mobile drilling rigs in the same way as emissions from a stationary source, such as a power plant's smokestack.

EPA representatives did not immediately return calls seeking comment Tuesday.

Industry groups have supported the rules — and warned that changing them could stifle oil and gas production.

Dave Galt with the Montana Petroleum Association said Tuesday that Schweitzer made the right decision to pull the state's request for approval. He said that avoided a looming legal dispute between the state and EPA over whether the rules were sufficient.

"It's a procedural issue, not a substantive issue," Galt said. "I think DEQ has done a great job of showing the value of that program to everybody."

Jeremy Nichols with WildEarth Guardians said the state's failure so far to prove the rules are sufficient to protect public health and the environment remained a problem.

"Montana created a bit of a mess here in trying to roll back these safeguards," he said. "I hope moving forward, we can clean up what's been done and also have an effective means of putting pollution in check that doesn't also involve looking the other way while these (oil and gas facilities) are being constructed."