WASHINGTON — The Obama administration on Friday will complete a generation-long effort to require insurers to cover care for mental health and addiction just like physical illnesses when it issues long-awaited regulations defining parity in benefits and treatment.

The rules, which will apply to almost all forms of insurance, will have far-reaching consequences for many Americans. In the White House, the regulations are also seen as critical to President Obama’s program for curbing gun violence by addressing an issue on which there is bipartisan agreement: Making treatment more available to those with mental illness could reduce killings, including mass murders.

In issuing the regulations, senior officials said, the administration will have acted on all 23 executive actions that the president and Vice President Joseph R. Biden Jr. announced early this year to reduce gun crimes after the Newtown, Conn., school massacre. In planning those actions, the administration anticipated that gun control legislation would fail in Congress as pressure from the gun lobby proved longer-lasting than the national trauma over the killings of first graders and their caretakers last Dec. 14.

“We feel actually like we’ve made a lot of progress on mental health as a result in this year, and this is kind of the big one,” said a senior administration official, one of several who described the outlines of the regulations that Kathleen Sebelius, the secretary of health and human services, will announce at a mental health conference on Friday in Atlanta with the former first lady Rosalynn Carter.