Moving to repair an immigration enforcement program that has drawn rising opposition from governors and police chiefs, senior immigration officials on Friday announced steps they said would focus the program more closely on deporting immigrants convicted of serious crimes.

In unveiling the changes, John Morton, the head of Immigration and Customs Enforcement, said the deportation program would continue to expand as planned in order to be operating nationwide by 2013, despite criticism from many police chiefs and from the governors of Illinois, New York and Massachusetts, who sought to withdraw their states.

But in making course corrections to the program, known as Secure Communities, Mr. Morton acknowledged the groundswell of local resistance, including opposition from Latino and immigrant groups, to an effort that is central to President Obama’s approach to controlling illegal immigration. Critics said the program was casting too wide a net and had strayed from its goal of bolstering public safety by expelling illegal immigrants who committed the most dangerous crimes.

In a fix likely to have broad practical effect, Mr. Morton issued a memorandum that greatly expanded the factors immigration authorities can take into account in deciding to defer or cancel deportations. Agents are now formally urged to consider how long an illegal immigrant has been in the United States, or whether the immigrant was brought here illegally as a child and is studying in high school or college.

In practice, the memorandum gives immigration agents authority to postpone or cancel, on a case by case basis, deportations of illegal immigrant students who might have been eligible for legal status under a bill stalled in Congress that is known as the Dream Act.

The authorities are also instructed to give “particular care and consideration” to veterans and active duty members of the military, especially if they have been in combat, and to their close relatives.

Mr. Morton also expanded the authority of federal lawyers who handle cases in immigration courts to dismiss deportation proceedings against immigrants without serious criminal records.

Also on Friday, Mr. Obama extended the deployment of some 1,200 National Guard troops who are backing up immigration agents along the Southwest border.

Under Secure Communities, tens of thousands of immigrants who were here illegally but had not been convicted of any crime were detained by local law enforcement and swept into deportation proceedings. Until now, once immigration agents in the field had started a deportation, government lawyers had little authority to decide which cases were worth pursuing in immigration court. Many immigration violations are civil, not criminal, offenses.

In the Secure Communities program, fingerprints of everyone who is booked into jail are checked against F.B.I. criminal databases, as has long been routine, and also against Department of Homeland Security databases, which record immigration violations. Homeland Security officials report results of fingerprint checks back to the arresting police departments, and federal immigration agents determine whether to detain the immigrants for deportation.

“We believe in this program, we think it’s the right program, and we intend to continue it,” Mr. Morton said on Friday. “But obviously we are listening to the concerns raised by the governors, members of Congress and community groups.”

Mr. Morton also said he would form an advisory commission of police chiefs, sheriffs, state and local prosecutors, immigration agents, and immigrant advocates. The first task of the commission would be to assess, within 45 days, another fix Mr. Morton is considering.

Currently all immigrants who are flagged in a Secure Communities fingerprint check can be detained for deportation by Immigration and Customs Enforcement agents from the time they are first booked into jail. Mr. Morton said that under his proposal, illegal immigrants who were arrested for minor traffic offenses, like driving without a license, and other minor misdemeanors, would not be detained for deportation until they were convicted of those crimes.

Mr. Morton also issued new guidelines he said would ensure that illegal immigrants detained by the police who were victims of domestic violence and witnesses to crimes would not be deported.

Immigration lawyers praised the new ground rules. “If these standards are applied consistently, it would allow ICE to focus government resources on dangerous criminals and national security risks to make America safer, a goal we all share,” said David Leopold, the outgoing president of the American Immigration Lawyers Association.

But several community groups rejected the changes as cosmetic tweaks that would do little to slow deportations that they said had separated immigrant families without reducing crime.

“This program is riddled with flaws and the announcement today acknowledges that,” said Chris Newman, general counsel of the National Day Laborer Organizing Network. He said the program should be suspended until the Homeland Security inspector general completes a review later this year.