WASHINGTON — The Obama administration on Wednesday announced a one-year delay in a major element of the new health care law that would allow small businesses to buy insurance online for their employees through the new federal marketplace.

It was yet another setback for the rollout of the health care law and resulted, in part, from the well-documented problems of the insurance marketplace website. Administration officials said they had to focus on the basic functions of the website, so that individuals could shop for insurance, before offering online enrollment for small businesses. In the meantime, businesses and their employees can apply through brokers.

Many employees of small businesses are uninsured, and the businesses themselves are much less likely than big companies to provide coverage to workers and their families.

The latest delay, coming just as the White House was boasting of major improvements in the health insurance website, HealthCare.gov, opens the door to more complaints about the health care law and could increase pressure to delay other provisions.