A highly promising blood test to detect most of the main forms of cancer with more than 95 percent accuracy has been developed and could be on the market in three or four years if large-scale trials are successful.

The test was developed at Pennsylvania State University's Hershey Medical Center, and the trials are now being planned by Warner-Lambert, a giant pharmaceutical company.

There has been disappointment after disappointment in trials of tests for early, still "silent," cancer. Based on results so far, however, the new test won unusual praise yesterday from the highly regarded Research Corp., a nonprofit group representing the university in licensing and patenting arrangements with Warner-Lambert.

The 68-year-old Research Corp. has been midwife to scores of advances, including the cyclotron (one of the first atom-smashers), lasers, cortisone-type drugs and vitamins A,B and B-12. "It is seldom that we see an invention with the potential for public benefit this one has," Dr. Willard Marcy, Research Corp. vice president, told a news conference here.

The test is a chemical assay for an unusual glycoprotein -- a protein rich in a so-called "sugar acid" called sialic acid -- evidently shed from the membranes of fast-dividing cancer cells as they grow.

This glycoprotein was discovered at the Hershey center by Dr. Eugene Davidson, chairman of biological chemistry, and Dr. Sally Bolmer. They first found it in mouse cancer cells grown in the laboratory. Then they found a very similar chemical in cultivated human cancer cells.

Then they found it in the blood of cancer patients.

There are other chemical tests, some highly useful, some not yet so, for specific cancers. To Davidson's and Bolmer's astonishment, they have found their glycoprotein in four major groups of cancers: carcinomas, sarcomas, melanomas and in the diseased lymphatic glands of Hodgkins disease.

"So far we have found it in at least 15 to 18 cancers," Davidson said. "At the moment there doesn't seem to be a significant difference dependent on the type of cancer."

In tests of blood from 300 cancer patients, the test proved 96 percent accurate. Applied to the blood of 250 apparently normal, cancer-free persons, the test gave a "false positive" result -- incorrectly indicated a cancer when there was none -- only 2 percent of the time, Davidson said.

He called these results "highly encouraging." These are good scores for a test to help tell doctors whether a suspected victim really has cancer, or whether a known cancer has been successfully treated.

They are also probably good scores for a test that might be used to screen suspects, high-risk populations, such as heavy smokers.

Warner-Lambert must now convert the Hershey glycoprotein assay into one that can be performed on a large scale. Then, starting late this year or in early 1982, the firm plans extensive human trials. Both these and ultimate marketing must win Food and Drug Administration approval.