The nation's Blue Cross and Blue Shield plans cut their costly hospital admissions by 9.5 percent from 1970 to 1981, while admission rates for the general population shot up 11 percent.

In large part, Blue Cross-Blue Shield did it by starting to pay for doctors' office and other non-hospital treatment on a massive scale, moving away from their old practice of paying mainly for expensive hospital care.

The achievement--and "savings of millions of dollars"--were described at a news conference here by Blue Cross-Blue Shield officials and confirmed by a Johns Hopkins School of Public Health study team.

They called the Blue Cross-Blue Shield payments one pattern of the future for all health insurors, including the federal government. Blue Cross-Blue Shield plans cover a third of all Americans, more than any other insuror, including Medicare.

Most of the country's 99 local and national Blue Cross and Blue Shield plans now pay for most outpatient care--care in doctors' offices and non-bed care at hospitals--said David Klein, Blue Cross-Blue Shield Association senior vice president.

Included to a varying extent in various plans and contracts are X-rays and lab tests, home care, nursing-home care, psychiatric care, surgical procedures and most care in doctors' offices, except routine physicals.

"We didn't halt health cost inflation, but I think we helped moderate it. And I think we've demonstrated that quality care can be delivered in a less costly setting," said Leonard Davis, senior director of Blue Cross of Greater Philadelphia.

That five-county plan is a leader in requiring that much surgery be done on a one-day basis.

The Blue Cross-Blue Shield officials made no nationwide estimate of savings. But in just 3 1/2 years, testified Dr. Monroe Lerner of Johns Hopkins, Philadelphia Blue Cross saved $15 million merely by ordering that most abortions, female sterilizations, ear-canal drainages and removals of impacted wisdom teeth be completed, and the patient sent home, in a day.

Specifically, said Lerner, Blue Cross-Blue Shield cost-containment programs--doctors' office payments and other measures--accounted for "at least 25 percent" of the reduction in hospitalization.

He said much of the rest of the credit must go to such factors as "more selective enrollment," the growth of "public payment plans" such as Medicaid, and increasing "cost-sharing," or making insured patients pay a greater share of their bills.

Such steps meant that the Blue Cross-Blue Shield plans avoided insuring some of the sickest patients and started making some people think twice before seeking hospital care.

Lerner said the Blue Cross-Blue Shield achievement in moving more and more care out of the hospital bed represents "a great change in behavior" on the part of both hospitals and doctors, and one that offers some hope for getting an even larger share of the national health bill under some control.

Also important, said Lerner and Johns Hopkins' Dr. David Salkever, were some, but not all, forms of "utilization review," especially case-by-case scrutiny of the need for hospital care, with denial of payment in unjustified cases.

From 1970 to 1981, the hospital admission rate for Blue Cross subscribers dropped from 125 to 113 admissions per 1,000 subscribers, while the rate for the general population under 65 (those not covered by Medicare) rose from 129 to 145 per 1,000.