People with knowledge of the administration’s work to put the law into full effect said the postponement was in part a result of delays by the I.R.S. and the Treasury Department in finishing proposed rules and regulations for businesses.

Catherine E. Livingston, who was the health care counsel at the I.R.S. until February, said the delay was “a recognition of practical realities.” Employers and insurers are supposed to inform the agency of the people they cover. But without the final rules, employers and insurers could not program their computers to comply, said Ms. Livingston, a lawyer at Jones Day, a Washington firm.

That uncertainty, in turn, fueled a campaign by employers lobbying for a delay. Business groups on Wednesday continued to praise the administration for the postponement, which mainly provided regulatory relief to businesses that already insure their employees. With the threat of penalties also delayed, larger businesses that do not cover their workers will be under no pressure to do so before 2015.

“With this temporary reprieve from a complex compliance regime, U.S. companies will have additional time to find workable solutions to these challenges while continuing to provide employees and their families with certainty and peace of mind about their employer-provided health insurance coverage,” said Gary W. Loveman, the chairman of Caesars Entertainment Corporation and the leader of a health committee of the Business Roundtable, which represents corporations.

While businesses played down the effects of the delay, Republicans played up what they saw as the political perils for Democrats as both parties tried to gauge the impact for 2014. Republicans portrayed Democrats as the party of big business interests for delaying the employer mandates while keeping in place the individual mandate requiring most Americans to have health insurance starting in January.

A nonpartisan expert, Professor Robert J. Blendon of the Harvard School of Public Health, said, “The delay will raise an issue of fairness: why would the administration give a one-year grace period to employers and not to employees?” In addition, he said, “this sends a signal politically that things are not going well and there may be problems ahead.”

Behind Republicans’ bravado is a party split over whether to propose alternatives to the health care law or to seek its repeal without any replacement benefiting the 49 million uninsured Americans — an internal debate that the more numerous pro-repeal conservatives have won for now. They united this week to characterize the delay as a ploy by Mr. Obama to help Democrats ahead of the 2014 elections.