WASHINGTON — U.S. and Iraqi negotiators have agreed on a draft security pact that would govern the presence of American troops in Iraq after January, Bush administration officials say, but its final approval is far from certain.

The draft calls for U.S. troops to pull out of Iraqi cities by the end of June next year and leave Iraq by Dec. 31, 2011, unless the Baghdad government asks them to stay. It also includes a compromise on the biggest bone of contention: legal immunity for American forces, according to the officials, who spoke on condition of anonymity to discuss the evolving diplomacy on the so-called Status of Forces Agreement.

The draft, reached after months of halting and often tense talks, contains elements that are expected to further aggravate an already difficult effort to get the Iraqi government and parliament on board.

It also may draw objections from U.S. lawmakers, whose support is not legally required but is considered essential to the eventual success of any deal, according to the officials.

However, the negotiating teams have decided they cannot improve on the proposal and have sent it to higher-ups for a political decision as time runs out on both the Bush administration and the U.N. mandate under which U.S. troops now operate, which expires on Dec. 31, they say.

Without an agreement soon, the officials said that the two sides will have to begin look more seriously at alternatives that include extending the U.N. authority.

The officials would not discuss the draft agreement in detail. Yet they did discuss the troop pullout dates and described in general outlines the provisions on legal immunity. Under the agreement, Iraqi authorities would have a limited role in the prosecution of off-duty U.S. soldiers accused of committing crimes off their bases, they said.

Meanwhile, civilian employees of the Defense Department would be afforded the same immunities granted to State Department workers under the Vienna Convention on Diplomatic Relations, the officials said.