A nationally known psychiatrist and microbiologist testified today that he does not believe improper diet caused the mental illness of a former psychiatric patient who has sued a Rockville hospital for $12 million.

Dr.Morris A. Lipton, a professor of pyschiatry, microbiology and nutrition who also is certified as a specialist in pyschiatry, microbiology and internal medicine testified in U.S. District Court here that James Bock's symptoms were inconsistant with the symptoms of someone suffering from reactive hypoglycemia - low blood sugar.

Bock who spent five years and $125,000 at Chestnut Lodge, a private psychiatruc hospital on 100 rolling acres in Rockville, has contended that all the while he was being treated for a psychiatric disorder relating to his relationship with his mother, he really was suffering from the metabolic condition.

In his malpractice suit against the hospital. Bock charged that psychiatrists there improperly failed to act ehen an analysis of his urine, performed within days of his admission in 1967, turned up a trace of sugar, a possible indicator of hypoglycemia.

Lipton testified today on cross-examination as did another of the lodge's witnesses yesterday that failure to follow up on the finding of a trace of sugar "is not the kind of medicine I would practice. If it was my case I would have repeated the test."

However, he continued, "my medical opinion is that Chestnut Lodge lucked out because of the absence of any" finding of sugar in urine tests one and two years later. The first finding was, he testified, "irrelevant."

Testimony during the first seven days of the trial, as well as the records of the lodge, indicate that Bock suffered from depression, suicidal impulses, anxiety, depression and a general run-down feeling.

After leaving theh Lodge in 1972 he was tested by an internist in Dallas, Tex. - Bock's home town - who told Bock he was suffering from hypoglycemia and put him on a special diet high in protein and low in refined carbohydrates such as white bread and refined sugar.

Bock has testified that within 10 days of going on the diet he was free of all his symptoms. Since that time has obtained a master's degree in accounting and hasbeen married for the past two years. Prior to going on the diet he was unable to complete studies in law school and was unable to have lasting relationships with women, according to testimony.

Lipton testified today that while he couldn't absolutely rule out the possibility that Bock suffered from hypoglycemia, he does not believe the test administered to Bock in Texas and later in the Washington area were valid.

On cross-examination by Bock's attorney, Kenneth M.Robinson. Lipton said that while the lodge should have repeated the urinalysis in 1967. "the poorquality of medicine represented by that . . . is very tivial indeed . . . as compared to Dr.(Guillermo) Guzman's failure to repeat" the test for hypoglycemia, "which to me is a gross error."

Guzman now Bock's brother-in-law, gave Bock the test in Texas but did not have Bock obserevd during the period of tasting to see if he had any physical symptoms to match his various blood sugar levels. Lipyon testified that as well as Guzman's giving Bock a medication the night before the test that can effect blood sugar levels invalidated the test results.

Bock has contended that he has fully recovered since going on the diet, but there has been testimony during the trial that he is suffering now from psychiatric complaints similar to thosethat led to his hospitalization