WASHINGTON — More than 120 insurance companies have signed up for online health exchanges that will start offering subsidized plans in less than four months.

Federal officials pointed to that number as an early sign of consumer choice and competition that could help limit costs and prevent the price hikes that Republicans and some analysts have forecast.

At the same time, two western states that had planned to operate their own health insurance exchanges have sought federal assistance, an indication of the hurdles states are confronting in implementing a mainstay of the Affordable Care Act (ACA).

New Mexico and Idaho had been two of the scant Republican-led states that were willing to run their own health exchanges for people who lack coverage. But the health insurance chairmen of both states said last month their computer systems will not be ready by the fall deadline.

Open enrollment for uninsured Americans to shop on the new exchanges begins October 1, with coverage taking effect at the start of next year. State exchanges are expected to draw 7 million enrollees and are regarded as the keystone of the ACA.

The call for help from Idaho and New Mexico gives the federal government responsibility for all or part of the exchanges in at least three dozen states. The ACA had envisioned each state running its own exchange but established a federal exchange as a backup.

For job-based insurance, the government issued a final rule giving companies more room to use employee wellness programs. The rule supports workplace health promotion and prevention as a means to reduce the burden of chronic illness, improve health and limit the growth of health care costs, while ensuring that individuals are protected from unfair underwriting practices that could otherwise reduce benefits based on health status.

The final rules continue to support “participatory wellness programs,” which generally are available without regard to an individual’s health status. These include programs that reimburse for the cost of membership in a fitness center; provide a reward to employees for attending a monthly, no-cost health education seminar; or reward employees who complete a health risk assessment, without requiring them to take further action.

The rules also outline standards for nondiscriminatory “health-contingent wellness programs,” which reward individuals who meet a specific standard related to their health.