When 84-year-old Nellie Long first visited Dr. Omar S. Zaki last February for a physical examination, she says, the Falls Church internist spent less than an hour poking and probing and talking to her. Then he billed her for $635.

Included in the itemized bill were an electrocardiogram and 14 laboratory tests, for which the physician charged $495.

Those same procedures would cost $224 in one of Washington's major teaching hospitals, and hospitals usually charge more than physicians for the same tests.

According to Frank Ferraraccio, executive director of the medical society of the District of Columbia, a charge of $635 is "way out of line. At most, a complete history and physical exam shouldn't cost more than $100, $150, including EKG and chest X-ray. With lab tests it shouldn't cost more than a couple hundred bucks."

"I have a right to charge her whatever I want," said Zaki, when asked about his bill. "It's a free enterprise system."

Last night, however, 36 hours after he was first interviewed, Zaki said, "looking back at it, (the high bill to Long) was a regretable mistake."

He said he has been practicing in the area for three years but since being contacted by a reporter is now "trying to find out what's the going rate" for medical services and plans to lower his fees accordingly.

Long, who lives with her husband on an income of $600 a month - less than Zaki's charge for her visit - says she "flipped" when she learned what the doctor had charged. "I called and asked if it was an error, and they said no, it was my bill. I said I didn't understand why it was that much. It was only a partial physical."

After she filed a complaint with the Fairfax County Medical Society, of which Zaki is a member, the physician agreed to accept whatever Medicare paid - which, after deductibles, came to $57.80, nine percent of Zaki's bill.

Zaki said he only reduced the bill because "the patient was not adequately informed" what the charges would be ahead of time.

"We tell the patient it's going to cost them that much," said Zaki, who threatened to sue a reporter and said "I have no reason to explain to some punk in the street what I do."

What Zaki does is charge as much as eight times the cost of a given laboratory test. For instance, one thyroid function test he ordered, for which American Medical Laboratories, Inc., charges $5, he charged $40. Medicare pays a maximum of $26.50 for the same test.

Information provided by Zaki's office could leave a patient ill-prepared for his bill.

A caller yesterday was told that an initial physical examination is rarely less than $70 or $80.

When asked what tests would cost, the woman then said the charges for the examination, EKG and blood tests would probably fall between $100 and $500. "Dr. Zaki," she said, "does not accept Medicare rates." Medicare pays $57 for a physical examination.

Dr. Omar S. Zaki was born in Iran, in 1945, and received his medical schooling at King Edward Medical College, Lahore, West Pakistan, according to the records of the American Medical Association.

AMA records show Zaki having licenses in eight states, including Virginia. He is not, however, a member of the AMA.

According to records on file with the American Board of Internal Medicine, in Philadelphia, Zaki was an intern at Morristown Memorial Hospital, in Morristown, N.J., from July 1967 to June 1968.

In July of that year Zaki began a first-year residency in internal medicine at New York City's Lenox Hill Hospital. According to hospital officials, however, he resigned and left the hospital in December, never completing the program.

On Aug. 6, 1971, he began what officials at St. Mary's Hospital in San Francisco, says was to have been a two-year residency in internal medicine. He left St. Mary's less than three months later, according to hospital records.

According to Barbara Loy, secretary to Dr. Joseph J. Furlong, who directs the internal medicine residency program at St. Mary's, Furlong wrote a letter in which he stated Zaki left "solely because of his inability to meet the strick state licensure requirements for foreign medical graduates in California." His work at the hospital, Loy said, "was perfectly satisfactory."

According to AMA records, Zaki has since been licensed in California.

From January to June, 1972, Zaki served as a resident in internal medicine at Miriam Hospital, Providence, R.I., according to the records of the American Board of Internal Medicine. He then spent a year of training at Boston's prestigious Peter Bent Brigham Hospital.

According to sources familiar with physician education, it is unusual for a doctor to hop around among programs, particularly at mid-year, as Zaki did.

Zaki said he left Lenox Hill "because I didn't like New York . . . the hospitals where I have privileges ran checks on me. Why are you doing this?"