Had Kathleen Watt not been sitting in the People's Drug Store in Woodbridge when Toby G. Long walked in on July 11, Dr. Peter G. Bourne might still be President Carter's chief adviser on health and drug abuse.

But Watt, an inspector for the Virginia State Pharmacy Board, was in the store for a routine inspection, and thus triggered a series of events that made 38-year-old psychiatrist a central figure in a criminal investigation, forced him from his influence position and created a political crisis for the Carter White House.

Watt said yesterday that she didn't realize who "Dr. Bourne" was when Toby Long presented the prescription for 15 tables of Quaalude, a frequently abused sedative, to a pharmacist in the Prince William County store. Watt said she became suspicious because the prescription bore a Washington address for Bourne and she wondered why it was being presented in Woodbridge, 35 miles south of Washington.

The inspector said she called a Washington telephone number on the prescription blank and reached a recording announcing that the number had been disconnected. She called information for a new number, and received one number instead of the two most physicians have.

After calling the new number and receiving no answer.Watt said she called Prince William County police to report a "suspicious event."

When police arrived at the store they seized the prescription, which turned out to bear a fictitious name, and charged Long with attempting to obtain a controlled substance by the use of a false name." Under Virginia law that is a felony that carris a maximum penalty of five years in prison and a $15,000 fine.

The implications of that action were apparent in separate areas yesterday:

Bourne, who resigned his $51,000-a-year White House post yesterday, gave another explantion of why he wrote the prescription for a fictitious person.

Prince William County Commonwealth's Attorney Paul B. Ebert said Bourne's statement Wednesday night, admitting he had written the name on the prescription, was an admission that Bourne had violated the same law Long is charged with violating.

Long, a friend of a Bourne aide for whom the drugs were intended was suspended with pay from her job as a physical therapist for the Prince William County schools, pending her trial in a county court.

When Bourne defended his action by citing Section 9 of the American Medical Association's Principles of Medical Ethics Wednesday, he cited only that portion of the section that was favorable to his case.

Various experts on medical ethics and psychiatric practice said they knew no reason for a doctor to use a false name on a prescription, especially because state and federal laws require the patient's name and address be used on prescriptions for controled substances, such as Quaalude.

Bourne said Wednesday night that when he wrote the prescription for Ellen Metsky, his administrative assistant and Long's roommate, he put a false name on the prescription because both he and Metsky "were concerned about the protection of confidentiality both with regard to her taking medication and to the creation of a record anywhere that she had been treated by a psychiatrist."

Yesterday, however, Bourne said that Metsky asked him for the prescription and he advised her to see a psychologist. He said she "just wanted to get some sleep," and that he suggested using the fictitious name.

Bourne said he was concerned because the Drug Enforcement Administration has access to records of prescriptions for controlled substances and also feared that Metsky might someday have trouble obtaining a security clearance if it appeared that she had been under a psychiatrist's care. "Things can come back to haunt you," he said.

"She was having a sleep problem," he said. "There were 50 million (methaqualone, the generic name for Quaalude) pills dispensed last year. I was asking for 15."

Bourne said he provides such help for friends on the White House staff because the White House doctor has "more than he can handle" and people have to "wait in line there."

The extent of Bourne's possible legal troubles remained unclear yesterday. Ebert, the Prince William County prosecutor, said he is "not going to prosecute him if his story is true, if it is one isolated incident. If it is not an isolated incident, and I feel evidence is sufficient, I will bring a charge."

According to Ebert, Bourne could be charged under one or two Virginia laws, one a felony, the other a misdemeanor.

It is a felony for anyone to get a controlled substance - in this case, Quaalude - "by the use of a false name."

It is a misdemeanor to commit "fraud, deceit and forgery," and anyone found guilty of violating that statute may be sentenced to up to a year in jail and fined up to $1,000.

Ebert said that anybody "involved in the transaction" of passing a prescription with a false name on it would be committing a felony.

He added that Bourne's claim of legal justification for issuing a prescription under such a false name was "sort of like mercy killing. He may have the best motives on earth, but the intent to kill still remains."

The prosecutor said he hopes to receive a report from the county's narcotics squad by next week, and will decide at that time whether or not to prosecute. He said he still has to do research on the legal mechanics of prosecuting a District physician who writes a phony name on a prescription submitted to a pharmacy in Virginia.

When Bourne made his defense Wednesday night he relied, in part, on Section 9 of the AMA's Principles of Medical Ethics, first issued 21 years ago.

"Section 9 of the Principles of Medical Ethics prevents a doctor from revealing the confidences entrusted to him, in the course of medical attendance," Bourne said. The ethical requirements of the American Psychiatric Association further require that 'even the identification of a patient must be protected with extreme care," he said in his statement.

However, the entirety of Section 9 of the AMA code reads: "A physician may not reveal the confidence entrusted to him in the course of medical attendance, or the deficiences he may observe in the character of patients, unless he is required to do so by law or it becomes necessary in order to protect the welfare of the individual or of the community."

Natalie Spingarn, executive director of the National Commission on Confidentiality of Health Records, said yesterday that "...apparent deception, even for high motives, can create more problems than it prevent . . .

"Material came out [in this case] that would never have come out" because of the use of a false name, she said. "In the eyes of the public it can distort the confidentiality of medical records," she said, adding that confidentiality is "important to the success of medical therapy."

Spingarn said the government-sponsored commission was unaware that any physicians use false names on presctiptions to protect patient confidentiality. "We get huge stacks of mail and I have not heard of this in our two years," she said.

"I have personally never known of this, I've never known of others doing it and it's never come to out attention," said psychiatrist Dr. Robert Moorer, the medical director of a private psychiatric hospital in San Diego and the immediate past chairman of the American Psychiatric Association's ethics committee.

Moorer said a physician may intentionally break the law as a conscious act of civil disobedience, as may any other member of society. But, like any other member of society, the physician who does so must expect to pay the penalty, Moorer said.

Dr. Jerome Beigler, chairman of the Psychiatric association's committee on patient confidentiality and confidentiality of records, said, "Confidentiality canbe protected within the dictates of the law. You just can't break the law."

Dr. Joseph Lifschutz, a psychiatrist in private practice in Berkeley, Calif., is familiar with the basic issues of patient confidentialty and right to privacy. Ten years ago Lifschutz spent three days in jail for contempt of court rather than reveal the fact that he had treated a particular patient, much less reveal what he and the patient discussed during an anaylsis session.

"I must confess that this is a new idea to me," said Lifschutz, when asked about the practice of putting a fictitious name on a prescription. "I have never heard of that being done . . . I would be very skeptical about that. I would not approve of that because I would feel that confidentiality can't really apply to medical prescriptions. I feel confidentiality is of the utmost importance in the verbal communications between the psychiatrist and his patient.

"The act of psychotherapy deserves confidentiality. Writing a prescription does not. I think the pharmacist must maintain confidentiality of his records but if [a physician] is writing a prescription for somebody I think he should put the patient's name on it."