Congress needs to give swift approval of subpoena authority for the presidential Oil Spill Commission in order for the panel to complete its investigation of the BP PLC oil spill, the leaders of the commission said yesterday.

The commission's co-chairmen, Bob Graham and William Reilly, are calling on the Senate to act this week so investigators can compel testimony from reticent companies involved in the spill and enable the panel to complete its report by the January deadline.

But lawmakers appear unlikely to move on the approval in the few days left before they head to their home states until after the November elections. Democratic and Republican Senate leadership aides indicated yesterday that speedy approval would be unlikely, each blaming the other party for the delay.

The commission's leaders say that without subpoena authority, they are getting the run-around from companies involved in aspects of the rig operation. BP owned the well, Transocean Ltd. owned the rig and drilling contractor Halliburton Co. performed services including sealing the well.

Investigators have "encountered resistance to full responses to their questions," Graham, a former Democratic senator from Florida, told reporters yesterday.

The White House-created commission is tasked with investigating the causes of the Deepwater Horizon disaster and reporting its findings and policy recommendations to President Obama by the second week of January.

Over the course of two days of public hearings in Washington this week, the oil spill commissioners have criticized the administration's response to the disaster.

Reilly blasted the Interior Department's moratorium on deepwater drilling, and he and Graham questioned whether the administration slowed its response to the spill initially based on a mistaken belief that less oil was spilling from the well. But yesterday's comments demonstrated a new level of frustration with lawmakers.

"It is unjustifiable for Congress not to give full authority for us to use all of the instruments of the investigative process to resolve this, for the one commission that is independent and has a national mandate," said Reilly, who led the U.S. EPA under President George H.W. Bush.

Graham said it was "stunning" that the commission lacks subpoena power.

The House gave overwhelming approval in a 420-1 vote in June to a bill granting subpoena powers. But the Senate has not yet acted.

Senate Majority Leader Harry Reid (D-Nev.) would like to clear the measure but has been held up by the GOP, according to his spokesman.

"If we could have gotten it through the Senate, we would have -- Republicans are balking," Reid spokesman Jim Manley said yesterday.

But a spokesman for Senate Minority Leader Mitch McConnell (R-Ky.) said he knew of no effort from Reid to call up the vote. Republicans supported efforts for a bipartisan commission with subpoena power in the Senate Energy and Natural Resources Committee and in a GOP oil spill bill, McConnell spokesman Don Stewart said.

Under those proposals, Congress would have set the membership for that commission, rather than the presidentially appointed panel that exists now. Some Republicans view Obama's commission as partisan.

As lawmakers duel over the issue, the commissioners say that precious time is being wasted.

"If we don't get subpoena power until the lame-duck session, which may be six, eight weeks from now, we will have lost an enormous amount of our ability to complete a full report within the time frame," Graham said.