WASHINGTON — In proposing a major expansion of offshore oil and gas development, President Obama set out to fashion a carefully balanced plan that would attract bipartisan support for climate and energy legislation while increasing production of domestic oil.

It is not clear that the plan announced Wednesday will do either.

While the oil industry, business groups and some Republicans offered muted support for the proposal, most environmental groups denounced it. And the senators whose support Mr. Obama is courting for highly contentious climate and energy legislation to be introduced in the coming weeks gave decidedly mixed reactions: For every senator who praised it as at least a partial answer to the nation’s energy needs, another raised alarms about befouled beaches and continued dependence on fossil fuels.

Even Mr. Obama sounded somewhat torn in announcing a drilling plan that would open large tracts of the Atlantic coast, the eastern Gulf of Mexico and Arctic waters off Alaska to oil exploration and eventual drilling.

“This is not a decision I’ve made lightly,” he said as he stood at Andrews Air Force base in Maryland on Wednesday near an Air Force fighter converted to burn renewable biofuels.