Asked in a questionnaire from the Senate Armed Services Committee what he would have done differently in Iraq if he had been defense secretary in the last six years, Mr. Gates responded: “War planning should be done with the understanding that postmajor-combat phase of operations can be crucial. If confirmed, I intend to improve the department’s capabilities in this area.”

He added that “with the advantages of hindsight, I might have done some things differently.”

He kept mainly to generalities in the 60 pages of answers to committee members’ questions. The White House sent the document to committee members on Tuesday.

The confirmation hearing is set for next week.

By criticizing the Iraq planning, however obliquely, Mr. Gates offered a glimpse of how he might distance himself from the record of the current secretary, Donald H. Rumsfeld, who will step down.

Mr. Rumsfeld has acknowledged mistakes in Iraq, but has dismissed criticism that too few American troops were dispatched to preserve order after Saddam Hussein’s fall in 2003.

Mr. Gates is scheduled be the sole witness at a one-day hearing next week that appears to be likely to speed him toward confirmation, Congressional officials from both parties said.

Even Democrats on the committee say that barring an unexpected disclosure Mr. Gates is likely to be approved by the Armed Services Committee and, soon thereafter, by the full Senate before it adjourns next month.

Mr. Gates’s carefully couched answers displayed few policy differences between him and the administration and, in many cases, states administration policy in anodyne language.

Several replies appeared fashioned to reassure that Mr. Gates is entering the job with a realistic assessment of its challenges and leaving open the possibility of changes in policy.

Asked whether the United States should engage in direct talks with Iran and Syria on stabilizing Iraq, Mr. Gates shied from endorsing bilateral overtures to either country.

“Engagement with Iran might well come as part of an international conference,” he said.

Talks with Damascus could “take the form of Syrian participation in a regional conference,” he added.

But he also said, “No option should be taken off the table,” noting that “even in the worst days of the cold war, the United States maintained a dialogue with the Soviet Union and China.”

A bipartisan commission led by former Secretary of State James A. Baker III and former Representative Lee H. Hamilton is widely expected to recommend an aggressive regional diplomatic initiative that includes direct talks with Iran and Syria. Mr. Gates was a member of that panel before resigning after his nomination.

His reply on Iran backed slightly from a study of which he was a co-author for the Council on Foreign Relations. The examination called for the United States to “engage selectively” with Iran, in part to dissuade Iran from pursuing nuclear weapons.

The administration has offered to hold direct talks only if Iran suspends its nuclear enrichment program.

“It is one thing to direct a study as a private citizen and another to serve as a senior policy maker,” Mr. Gates said.

Senator Carl Levin, the Michigan Democrat who will become chairman of the Armed Services Committee in January, said in an interview he intended to question Mr. Gates carefully about his willingness to challenge Iraq strategy in internal administration discussions, something that Mr. Levin said had not been welcome at the top levels of the administration.

In a private meeting this month, Mr. Levin said, Mr. Gates “assured me that this is the approach he will be taking.”

Mr. Gates, former director of the Central Intelligence Agency, signaled that he would re-examine Mr. Rumsfeld’s efforts to build up intelligence gathering at the Pentagon and its use of special forces for counterterrorism operations.

Mr. Gates and other C.I.A. veterans have criticized that policy.

“Clearly, if confirmed, this will be an area that I would look into,” he wrote.

Mr. Gates told the committee that he backed Mr. Bush’s decision to invade Iraq in 2003. In response to a question noting that nonconventional weapons were not found, he said: “I believe the use of pre-emptive force should be based on very strong evidence. It is a decision that must not be taken lightly.”

He defended the decision in 1991 by the first President Bush, for whom Mr. Gates was deputy national security adviser as well as intelligence director, not to push to Baghdad, after forcing the Iraqi army from Kuwait.

“I do not believe we were mistaken,” he said. “The coalition had not planned for, or resourced for, military operations to occupy Iraq.”