D.C. Police Chief Burtell M. Jefferson, troubled by persistent rumors of cheating on the last promotional test, told the 4,000 members of the department yesterday that he believes the rumors are "baseless" and were started by those who did not do well on the test.

". . . Rumors are amplified as they are retold and it becomes very tempting to believe them because they can be a private source of comfort," Jefferson said in an "Operation Candor" videotape presented at roll calls. "I have not seen even the smallest scrap of evidence to support the rumors."

Jefferson's presentation lasted about 10 minutes and described the safeguards surrounding the preparation of the tests. The most prevalent rumors, which have been sweeping through the department for over a month, allege that selected black officers were handed advance copies of the test in order to assure their rise in a department now dominated in the higher ranks by white officials.

The chiefs decision to go ahead with the "Candor" message follows a report on the rumors last Friday in The Washington Post.Early last week, informed sources reported that Jefferson had canceled his planned "Candor" message to avoid contributing to any publicity on the rumors.

POlice Inspector Marty Tapscott,head of an organization of about 40 ranking black police officials, has called the rumors of cheating racially motivated.

"The first time that blacks do well as a group on these promotional tests is accompanied for the first time by serious rumors that tests were leaked in advance," Tapscott said in a letter to The Post early this week. "These rumors are clearly saying that blacks are still considered intellectually inferior to whites and that blacks could have done so well only by having the tests leaked to them. This a rascism - period."

Jefferson and Tapscott said publiclythat they had not conducted any investigation into rumors, but would if they received any evidence.

In an interview late last month, Jefferson said that he believed it was "an impossibility" that a test had been leaked in advance, and he could stop the rumors by explaining how the test procedure worked.

In his taped message Jefferson explained that three captains, Charles Shuster. Clay Goldston and William Harlowe, had compiled the tests questions, working in a room provided by the Civil Service Commision. Only the captains had keys to the room and double-locked storage cabinets in it, Jefferson said. No one captain was permitted to work on the test alone, he said.

Their 600 proposed questions were winnowed down to the final 231 after a review by the department's deputy chiefs and former assistant chief Tilmon B. O'Bryant. This review by senior officials was conducted in the presence of one of the three captains, Jefferson explained.

The testsM which cover promotion to sergeant, lieutenant and captain, were printed, issued and graded by the Civil Service Commision, Jefferson said.

"I want to take this opportunity to express my confidence in all the persons that look part in our promotional process," Jefferson said. ". . . Nothing is being hidden."

A dozen officers interviewed outside the 3rd District station at 1624 V ST. NW yesterday afternoon said that they generally were reassured by the remarks of their chief. Said one: "You get three captains together and nothing [improper] is gonna happen because their future is at stake."

Former police chief Maurice J.Cullinane started the practice of spending "Operation Candor" videotapes to the stations in order to explain new policies in a more personal way.