The Obama administration on Friday issued a proposed rule governing hydraulic fracturing for oil and gas on public lands that will for the first time require disclosure of the chemicals used in the process.

But in a significant concession to the oil industry, companies will have to reveal the composition of fluids only after they have completed drilling — a sharp change from the government’s original proposal, which would have required disclosure of the chemicals 30 days before a well could be started.

Oil and gas companies will have to capture toxic and climate-altering gases from wells, storage sites and pipelines under new air quality standards issued on Wednesday by the Environmental Protection Agency.

The rule is the first federal effort to address serious air pollution associated with the natural gas drilling process known as hydraulic fracturing, or fracking, which releases toxic and cancer-causing chemicals like benzene and hexane, as well as methane, a powerful greenhouse gas.

The oil giant Shell filed suit in federal court in Alaska last week against a dozen environmental groups, employing a rare — and rarely successful — legal gambit in an effort to pre-empt anticipated legal challenges to its plans to begin exploration in the Arctic Ocean this summer.

Was the unusual maneuver an act of bravado, even desperation, by a company fearful that it might be thwarted again in its efforts to begin drilling in the seabed off Alaska’s North Slope?

Impatient with the slow pace of international climate change negotiations, a small group of countries led by the United States is starting a program to reduce emissions of common pollutants that contribute to rapid climate change and widespread health problems.

Secretary of State Hillary Rodham Clinton plans to announce the initiative at the State Department on Thursday accompanied by officials from Bangladesh, Canada, Ghana, Mexico, Sweden and the United Nations Environment Program.

The Environmental Protection Agency unveiled new standards on Wednesday sharply limiting emissions of mercury and other toxic pollutants from the nation’s coal- and oil-burning power plants.

The new rule, unless blocked by Congress or the courts, will be the first time the federal government has enforced limits on mercury, arsenic, acid gases and other poisonous and carcinogenic chemicals emitted by the burning of fossil fuels.

It will require all countries to reduce emissions that contribute to global warming

Two weeks of contentious United Nations talks over climate change concluded on Sunday morning with an agreement by more than 190 nations to work toward a future treaty that would require all countries to reduce emissions that contribute to global warming.

The State Department’s inspector general will conduct a special investigation of the handling of the pending decision on the proposed Keystone XL pipeline in response to reports of improper pressure on policy makers and possible conflicts of interest, according to documents released on Monday.

The Interior Department formally cited BP and its two chief contractors on Wednesday for numerous safety and environmental violations in the operation of the doomed Deepwater Horizon well.

BP, running weeks behind schedule and tens of millions of dollars over budget in trying to complete its troubled Macondo well in the Gulf of Mexico, took many shortcuts that contributed to the disastrous blowout and oil spill there last year, federal investigators concluded in a report released on Wednesday.

President Obama abandoned a contentious new air pollution rule on Friday, buoying business interests that had lobbied heavily against it, angering environmentalists who called the move a betrayal and unnerving his own top environmental regulators.

The president rejected a proposed rule from the Environmental Protection Agency that would have significantly reduced emissions of smog-causing chemicals, saying that it would impose too severe a burden on industry and local governments at a time of economic distress.