The nation's largest health insurer, Blue Cross and Blue Shield, recommended yesterday that its members stop paying for routine hospital tests that cost $1.5 billion annually.

More than 90 percent of all hospitals give the tests routinely upon admission, whether or not a doctor orders them.

Blue Cross-Blue Shield said some routine tests may still be given to surgery patients, but should be given medical patients -- 55 percent of all admissions -- only when the patient's doctor says they're needed.

The recommendation was backed by both the American Hospital Association and the American College of Physicians. It was the second, but by far the most important, recommendation in a "medical necessity" program started by Blue Cross-Blue Shield in 1977.

If successful, it could help moderate the countrys' rapidly escalating health bill, currently approaching $200 billion a year. Approximately 112 million Americans are covered by 130 local Blue Cross and Blue Shield plans. Other insurers commonly follow Blue Cross-Blue Shield procedures.

"There will be an educational or grace period of six months to a year, then we expect most of our plans will stop paying for these routine tests," said Walter McNerney, president of the National Blue Cross and Blue Shield Associations.

There was a day when routine testing upon hospital admission -- for example, taking a routine chest X-ray to detect tuberculosis -- was considered good medical practice, McNerney explained.

But now, he said, a whole battery of routine tests is obsolete or unneeded for most patients and may sometimes be harmful.

In "good medical practice," testing should be ordered individually and "complement, not replace, careful history-taking and physical examination," said the American College of Physicians, the main group representing specialists in internal medicine. "Injudicious" testing contributes greatly to the high cost of medical care, the college said.

The six tests most often given patients on admission are: chest X-ray, blood count, urinalysis, electrocardiogram, blood test for syphilis, and "SMA-12," which subjects one blood sample to 12 chemical analyses. If all six are given, the average patient's bill will run $60 to $70, Blue Cross-Blue Shield said.

Some hospitals give as many as 16 tests on admission.

Blue Cross-Blue Shield also said it will no longer recommend payment for 26 other laboratory tests considered "outmoded, unnecessary, unreliable or of no proven value," unless a doctor can show they are necessary.

But most of these tests are no longer widely used. In 1977 Blue Cross-Blue Shield issued a similar list of 42 surgical and diagnostic procedures for which it would no longer recommend payment, unless justified.

The estimated annual saving in eliminating those 42 procedures was $27 million a year, and the 26 tests now placed in the same class probably add up to no more than $100 million a year on patient's bills.

"But in routine admission testing," said McNerney, "a significant change will mean a lot of money. And we hope that a ripple effect -- in which hospitals and physicians look hard at a lot of the things that they do -- will be even more important."