Ronald Reagan's health advisers are urging creation, on a "trial" basis, of a new, voluntary, paid health insurance system for the estimated 1 million Americans whose infirmities or disabilities make them "uninsurable."

Their proposal is similar to one part of a more general catastrophic health insurance plan for "high risk" persons that was tentatively approved by the Senate Finance Committee last March. But it is much smaller in scope than that Senate Finance plan, which in turn was a cut-down version of national health insurance schemes urged by Sen. Edward M. Kennedy (D-Mass.) and to a lesser extent by President Carter.

Under the proposal, which was devised by the insurance industry, all health-insurance underwriters in each state would be required to make coverage to uninsurables available on a nonprofit "pool" basis. These people would pay premiums. Subsidies -- if these premiums turned out to be too low -- would be shared by the carriers and, ultimately, those enrolled in regular health insurance plans.

One way or another, the public bears the cost of care of the uninsurables, Dr. William B. Walsh, chairman of Reagan's Health Policy Advisory Group (HPAG), said in a two-hour interview in his Bethesda office yesterday.

Moreover, he said, any needed subsidies would be very small, on the order of 25 cents a month for each policyholder, and the cost to the federal government would be nil. He said the idea has had an encouraging five-year tryout in Connecticut.

Walsh, president of Project Hope, an international medical education organization and health-policy "think tank," also discussed several other recommendations made by HPAG and embodied in a report he delivered late Friday to the presidential transition team. These included urging the White House to consider:

Enabling persons covered by Medicare and Medicaid to choose annually from among coverage plans to be offered by competing private carriers.

Walsh said that the government, while paying the premiums, would in effect be enlisting the competing carriers to police fraud said to amount to billions of dollars annually.

Scrutinizing Professional Standards Review Organizations, which, in trying to prevent excessive or needless hospitalization under Medicare and Medicaid, are "spending $1.80 to save $1," and the federally financed -- and supposedly community-based -- health-service agencies, which try to curb excess hospital beds, with a view to decentralizing them.

Designing a home health-care "extender" system that, in creating a relatively inexpensive alternative to avoidable hospitalization and confinement in nursing homes under Medicare and Medicaid, would hire otherwise idle elderly persons to go into the nearby homes of other elderly who are enfeebled or sick and provide hot meals, baths, and other services.

Reagan, at a private meeting with Walsh in Los Angeles last May, asked him to head what came to be known as HPAG. "We had known each other casually for a long time, and Reagan was once the Project Hope honorary chairman in California," Walsh said.

He recalled Reagan telling him at the May meeting:

"If there's one thing I want you to come up with, it is, provide me with suggestions as to how we can cover the uninsured, the underinsured, and the marginally insured -- you know, improve their lot.I don't care whether they are Democrats or Republicans. I don't care if they are committed to support me. I just want you to call in the best brains available to solve these problems.'"

Walsh and Reagan adviser Martin Anderson together chose 15 specialists to serve on the HPAG, which assembled a stack of background papers, held a series of meetings, and, finally, agreed on positions summed up in the report to the presidential transition team.