John H. Sewell has been removed from the command sergeant major's program at Fort Belvoir and appointed a sergeant major. In some editions yesterday, it was incorrectly stated he was reduced in rank.

When he was an Army platoon sergeant in Vietnam, John H. Sewell says, some of his men smoked so much marijuana that sometimes he had to risk his life to walk them to their firing positions.

That made an impression, he said: "Me and drugs don't get along in any fashion."

Now, Sewell, 46, is on the other side of the fence. Accused of being soft on drug users by improperly exempting a sergeant from a mandatory urine test, he was relieved of duty as a command sergeant major at Fort Belvoir this week by his base commander and reduced to staff sergeant with restricted powers. His 27-year career, he said, is ruined.

The official charge is negligence on duty, and Army officials say Sewell made one bad decision.

But Sewell, who lists a Bronze Star among his numerous decorations, said yesterday the penalty is "extremely excessive."

He sees himself as a victim not of the Army's crackdown on drugs, but of "someone's hidden agenda."

"This stinks," he said. "I smell a rat."

"We're playing hardball," said Lt. Col. John E. Ooley, an Army spokesman at Fort Belvoir. "Every- body who comes in the Army knows they are putting their careers in jeopardy if they fool with illegal drugs."

Before the events of this past spring, Sewell had climbed to the highest rank and designation an enlisted man can hold: He was command sergeant major of the Army's 30th Engineer Battalion.

Until last month, he said, he was the only black command sergeant major at Fort Belvoir. Along the way, he collected honors that included a Meritorious Service Medal, the Army's third highest peacetime award.

Sewell said his years in the Army included only one blemish: he punched a man in 1963, fracturing his jaw, after the man used a racial slur against him.

Army officials said that his record since coming to Fort Belvoir last year had been trouble-free.

The Army will not comment on the specifics of the case, which Sewell is appealing. Sewell said the investigation began after he excused a new sergeant from a mandatory drug-detecting urine test in April.

A letter to Sewell from Belvoir's commander, Gen. Richard Kem, relieving him of duty as a command sergeant major said he acted "in clear contradiction of your commanding officer's policy that no one in the unit would be exempt" from the drug test. "You then failed to inform the commander of your action," the letter read.

The general also said it was likely that Sewell had acted after the sergeant had told him he was using illegal drugs and that "compounds the seriousness of this offense."

Sewell said the standing policy was that all new arrivals at Fort Belvoir should do nothing but "in process" -- get settled on the base -- so they could be ready for duty, with no classes, cleanup details or other distractions. Sewell said he believed the order applied to drug tests as well.

As for the accusation he may have harbored a drug user: "I'm not one of those educated people, but I've got a whole bunch of words I can use for that," he said.

Sewell said he knows the sergeant in question only slightly, and had no reason to cover up for him. He said he was in Texas "witnessing the birth of my first grandchild" when the sergeant was excused from the test. The test, when eventually administered this summer, showed the sergeant was using drugs, he said.

Three of Sewell's men -- none of whom would allow his name to be used -- described him as a tough but fair leader, resented by some officers for his power, but also a role model for the blacks who make up nearly two-thirds of the battalion.

"He was hard to live with, but that's what you need in the Army," one said. "He was a damn good command sergeant major." Another described him as "a very professional individual."

Sewell said he believes the Army's campaign against drug use is being used as an excuse in his case.

He also said "there are too many adverse actions with extreme penalties against senior black non-commissioned officers" at Fort Belvoir to be coincidence.

Two blacks in the unit also brought up the racial factor, without being asked.

The unannounced urine tests are part of the Army's recent well-publicized campaign against drugs. Although the Army began using urine tests in 1972 in Vietnam, administered under a program called "Operation Golden Flow," it was only three years ago the tests began being used as evidence in discharging a member of the service.

Of the 800,000 tests the Army administers each year, about 5 percent are positive, according to Army spokesman Elaine Henrion.

In May, the Army began random drug tests of Army reservists and national guardsmen in sensitive jobs. The Army hopes to begin testing this fall of some civilians in security jobs. The crackdown allows commanders to conduct unannounced searches with drug-sniffing dogs. The Army also is giving new attention to its drug treatment program, which offers help ranging from group counseling for first-time offenders to hospitalization for more serious cases.

Whether or not he is cleared, Sewell said he will ask for retirement as of Feb. 1. He said he no longer could command the respect of his men -- vital for a command sergeant major -- and that his family is shattered.

"The damage is done," he said. "You're talking 27 years of a person's life that's being shot up in smoke."