With U.S. Senate passage on Thursday of a landmark bill to crack down on Wall Street, lawmakers must resolve differences between that measure and one approved in December by the House of Representatives.

The Senate and House need to approve an identical bill before one can go to President Barack Obama to be signed into law. With the stakes high, it seems certain they will do so -- one way or the other.

Here's a look at how Congress can seek to resolve differences between its two chambers on legislation.

* The House and Senate could create a conference committee, composed of both Democrats and Republicans, to iron out differences between their respective bills. After an agreement is reached, it would go back to the House and Senate for final passage.

According to the Senate historian's office, that is how about a third of all legislation is reconciled.

With Democrats controlling the House and Senate, their leaders will decide whether to go to conference. Democrats say that would be their preference.

But if Democrats figure Republicans will raise procedural hurdles -- or that negotiators will be unable to reach an agreement in conference -- they could take another route.

With relatively simple bills, conference committees can wrap up their work within days if not hours. With complicated legislation like the regulatory reform bill, it could take weeks. Still, that would likely be the quickest way forward.

* One alternative option, which has become increasingly popular, is called ping-ponging. Under this method, the House and Senate bounce a bill back and forth to each other, making changes until there is a final agreement both chambers can pass.

* Another possibility would be for the House to pass the Senate bill -- or for the Senate to pass the House bill. But with big differences between the two chambers on financial regulation, that seems impossible on the pending legislation.

* Obama won final congressional passage of his landmark overhaul of U.S. healthcare this year after House and Senate Democrats used still another tactic. First, the House passed the Senate bill, which Obama signed into law, and then the Senate approved a package of changes demanded by the House. Obama signed that into law too.

(Reporting and writing by Thomas Ferraro; Editing by Peter Cooney)

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