OTTAWA-- An RCMP officer with Prime Minister Jean Chretien's protection staff says he was denied promotion because he is black. His complaint, lodged with the Canadian Human Rights Commission, could become another high-profile testing ground for a sensitive area of discrimination law.

Const. Calvin Lawrence, a 16-year RCMP veteran, has never faced racial insults or harassment at work. But when he was denied promotion to corporal, he made what his lawyer calls an ``adverse inference.''

IN LAWRENCE'S view there is no logical explanation why he wasn't promoted, so he concluded the reason must be racism.

``What other explanation could there be?'' asks Peter Barnacle, Lawrence's lawyer.

Before his current troubles, Lawrence was enjoying a fine career as a mountie. Laurence's expertise in special security was recognized in 1989 when he was given awarded a position p.rotecting the prime minister. At that time he also became a personal protection instructor for other RCMP officers.

In February 1992 the RCMP upgraded his position to corporal. Lawrence, 45, was assured that rather than hiring a corporal to replace him, he himself would be allowed to compete for the newly reclassified job. But the promotion never came.

The RCMP said in a prepared statement that it is ``committed to providing a working environment in which all individuals are treated with respect and dignity and where everyone has the right to work in a professional atmosphere which promotes equal opportunity and prohibits discriminatory practices.''

The RCMP offered no further comment.

Lawrence's complaint echos that of physicist Chander Grover, who fought a gruelling seven-year battle against his employer, the National Research Council.

Two years ago, Grover convinced a human rights tribunal that he was the victim of racial discrimination even though the question of his race had never been raised at his workplace. Because the NRC could not come up with any plausible explanation for its treatment of Grover -- why, for example, it denied him research and travel privileges -- the tribunal agreed the motivation likely was racism.

SOCIAL TABOOS have made open racism less common than it was several decades ago. ``It's pretty hard to find a smoking gun,'' said Barnacle, Lawrence's lawyer.

Because racism more often than not is subtle and hidden, human rights tribunals will examine circumstantial evidence that over a period of time can reveal a pattern of discriminatory behavior.