If George W. Bush were a candidate for a White House job or a Cabinet post today, he would have to answer a question that he has been unwilling to address.

White House employees and senior presidential appointees are required to answer "yes" or "no" to an employment form question that asks if they have illegally used marijuana, cocaine, crack cocaine, hashish, narcotics, amphetamines, depressants, hallucinogens or prescription drugs.

"Your answers must go back to your 18th birthday," the worksheet handed White House appointees instructs.

Texas Gov. Bush, the front-running Republican presidential candidate, told reporters last week he has not used any illegal drugs since at least 1974, when he was 28. He has refused to discuss the issue since, saying voters could make the decision about his fitness for office.

Some critics think Bush may have a hard time avoiding charges that he has set up a double standard when it comes to past drug use and government employment. "Anybody applying for a position in his administration presumably would have to answer the questions that Bush thinks are improper to ask," said Eric Sterling, president of the liberal Criminal Justice Policy Foundation.

But C. Boyden Gray, who was White House counsel when Bush's father, George Bush, was president, argued that the younger Bush is within his rights not to answer such questions publicly, because background forms filled out by government employees are considered confidential.

"I don't think he ought to have to answer publicly questions that aren't asked publicly of any of his potential appointees or of reporters," Gray said.

Federal agencies treat drug use issues seriously, in part because people with histories of drug use can be vulnerable to blackmail and other problems that could endanger government operations, classified documents and even the security of the president.

But the rush of baby boomers into government jobs has complicated what can be viewed as acceptable drug use. During congressional hearings in 1993, for example, it was disclosed that the Secret Service had balked at granting permanent passes to about a dozen White House staff members because of concerns about their drug use within the previous five years.

Gray said that during his tenure in the Bush administration, applicants were disqualified from senior positions if drug use had occurred within the previous 15 years. That standard was reduced to 10 years because Bush administration officials found casual drug use so common among those in the baby boom generation.

The Bush administration did not treat individual cases differently, Gray said. Drug use was "virtually disqualifying," no matter whom it involved, he said.

The Clinton White House, which has asked appointees to disclose all drug use going to back to age 18, does not immediately disqualify someone who has used drugs. "At the White House, decisions about suitability for employment are made on the basis of answers to a number of questions, which would include questions about drug use. But judgments are made on a case-by-case basis," spokesman Barry Toiv said.

The government essentially classifies would-be hires in three categories:

* "Non-sensitive positions" that have no access to classified or secret documents.

* "Public trust," which requires good conduct and character and usually involves skilled jobs, such as air traffic controllers, loan officers and prison guards.

* "National security positions," reserved for senior government jobs, particularly those that require security clearances.

The questionnaire for non-sensitive positions asks job applicants if they have used illegal drugs within the last year. The forms for the two other categories ask if the job applicant or political appointee has used drugs in the last seven years.

White House employees and presidential appointees requiring Senate confirmation, though, are instructed to ignore the seven-year limit and disclose any drug use or alcohol abuse going back to age 18.

The Clinton White House supplemental instructions add, "List and explain if you have ever abused any legal/prescription drugs to the point of dependency. In addition, list any treatment for drug and/or alcohol abuse."

Persons selected for White House jobs undergo review by the White House security office and undergo interviews by FBI agents, who raise questions about drug use during their background checks.

Federal agencies have wide leeway in deciding what standards to set for past drug use and how much time and money to invest in background investigations.

Not surprisingly, the Drug Enforcement Administration takes a dim view of past use by prospective agents. DEA requires applicants to list all previous drug experience, including the names of all drugs used and the dates of use.

There is a "degree of subjectivity" regarding past marijuana use at the DEA that allows for "youthful indiscretions," according to agency spokeswoman Rogene Waite. But use of any drugs beyond marijuana, without a prescription, is an automatic disqualifier.

A little marijuana use long ago would not derail a job applicant at the Federal Bureau of Investigation, but anything beyond a casual puff in college would likely be regarded as serious.

Would-be FBI agents are automatically disqualified if they: have used marijuana within the previous three years; have used marijuana a total of 15 times; have used any other illegal drug in the previous 10 years; have used any other drug more than five times; have sold any illegal drug for profit; or "used illegal drugs, no matter how many times or how long ago, while in a law enforcement or prosecutorial position, or in a position that carries with it a high level of responsibility or public trust."

The rules are somewhat more flexible at the Central Intelligence Agency, where officials employ a "whole person criteria." CIA agents--and anyone else granted access to classified materials--are governed by a director of Central Intelligence directive that suggests that any past drug use could be disqualifying.

But it also says several factors should be taken into account when assessing an applicant, including if the drug use was "not recent," "isolated or aberrational," or whether the user has demonstrated an "intent not to abuse any drugs in the future" or completed a drug treatment program and been granted a solid prognosis for staying clean and sober.

While confessing to a particular indiscretion may not hurt job chances at some agencies, someone caught trying to cover up drug use could be fired and perhaps even criminally prosecuted.

Staff writer Dan Balz contributed to this report.

CAPTION: Gov. Bush has not answered the question put to top appointees.