While President Obama’s decision about sending more troops to Afghanistan is primarily a military one, it also has substantial budget implications that are adding pressure to limit the commitment, say senior administration officials.

The latest internal government estimates place the cost of adding 40,000 American troops and sharply expanding the Afghan security forces, as favored by Gen. Stanley A. McChrystal, the top American and allied commander in Afghanistan, at $40 billion to $54 billion a year, said the officials.

Even if fewer troops are sent, or their mission is modified, the rough formula used by the White House, of about $1 million per soldier a year, appears almost constant.

So even if President Obama opts for a lower troop commitment, Afghanistan’s new costs could wash out the projected $26 billion expected to be saved in 2010 from withdrawing troops from Iraq. And the overall military budget could rise to as much as $734 billion, or 10 percent more than the peak of $667 billion under the Bush administration.

Such an escalation in military spending would be a politically volatile issue for Obama at a time when the government budget deficit is soaring, the economy is weak and he is trying to pass a costly health care plan.