Before the Pentagon begins reducing troop levels in Iraq (search) next year it probably will increase them this fall to provide extra security for a planned October referendum and a December election, a Pentagon official said Monday.

Lawrence Di Rita, Defense Department spokesman, noted that troop levels were raised last January during Iraq's first elections, and then returned to the current level of about 138,000 several weeks later.

"It's perfectly plausible to assume we'll do the same thing for this election," he said, while stressing that no decisions have been made.

Di Rita said he did not know how many extra troops might be needed during the referendum and election period.

Last January the U.S. troop level rose as high as 160,000. This was accomplished mainly by overlapping some of the units arriving in Iraq to begin a one-year tour with those who were finishing up their yearlong tours. In one case an Army brigade was kept a little longer than its scheduled 12 months in Iraq, and Di Rita said he could not rule out that this could happen again this fall, although the intention is to avoid tours longer than 12 months.

"The units that are there have been told to expect that: that it's possible that your planned rotation dates back to the U.S. will be affected by the need to keep a higher level for a longer period of time. They understand that," he said.

U.S. commanders see a likely need for extra troops this fall because the insurgents have tended to intensify their attacks as key political milestones approached. If a draft constitution is ready by Aug. 15, as intended, then a national referendum on the charter is to be held Oct. 15, followed by December elections based on the constitution.

Di Rita said the number of extra U.S. troops needed for the fall voting would depend in part on the readiness of newly trained Iraqi security forces.