Jefferson W. Lewis, the assistant D.C. fire chief considered by many to be the logical successor to retiring Chief Burton W. Johnson, is facing stiff opposition from the union that represents the city's firemen.

"The members of the union do not hold Jefferson Lewis in high esteem," said David Ryan, president of the Firefighters Association of the District of Columbia in a telephone interview yesterday.

Ryan said the labor group has no favorite candidate for the chief's position, but would not welcome selection of Lewis. Several sources suggested that union opposition to Lewis could boost the chances for Assistant Chief John T. Devine, who also is believed to be a top candidate for the job.

Union opposition is only one of several factors Mayor Walter E. Washington will have to consider in choosing a replacement for Johnson, whose retirement on disability stemming from an accident 35 years ago is scheduled to become effective within the next two weeks.

The mayor, appearing at a farewell party for Jefferson yesterday at a city firehouse, declined to give any indication of when he would announce his choice or to list major contenders for the job. He said only that he plans to examine the background of all 41 men who are technically eligible - two assistant chiefs, six deputy chiefs and 33 battallion chiefs - before making his decision.

At one point during the 90-minute farewell and awards affair at the No. 4 fire station on Sherman Avenue NW, the major mistakenly referred to Lewis as Chief Lewis, which some took to be a subliminal suggestion that Washington already has made up his mind.

Referring to Johnson, the mayor first called him Chief Lewis, the "Chief Jefferson" and finally Chief Johnson. That appeared to be less of a veiled suggestion than a case of confusion casued by the similar names of three chiefs involved: Burton (Burt) Johnson is fire chief, Bertell (Bert) Jefferson is a police chief and Jefferson Lewis is assistant fire chief.

Johnson's pending retirement has been known in the department for months, but a choice of his successor is not likely to come as quickly as the filling of the police chief's job. Washington chose Jefferson only hours after former chief Maurice J. Cullinane announced his plans to retire.

Amony the factors that must be considered is a feeling among some government leaders and community representatives voiced over the past five years that the heads of the police and fire departments should not be of the same race. Johnson, who is black served while Cullinane, who is white, was police chief.

Last month, Jefferson succeeded Cullinane and in so doing became the city's first black police chief. That set the stage for the appointment of a white to succeed Johnson, if the old system is to be kept.

Although Devine is white and Lewis is black, city hall sources claim that union opposition to Lewis is not based on race, but rather on the concern of union members' about Lewis' administrative skills.

"Lewis is no more an administrator than I am a jet pilot," one fireman said yesterday.

For the past four years, the 58-year-old Lewis has been responsible for supervising the operations of the 1,450-member fire department, while Devine, 46, has run been in charge of administrative chores. In the absence of Chief Johnson, Lewis has acted as chief.

Lewis said in a telephone interview yesterday that he has not "been concerned one way or another" with the union opposition to him.Asked if he thought it were racial, Lewis responded, "You can form your own conclusions, but at this point I don't think I'm going to enter into any controversy."

One source close to the mayor said that race probably will not be a factor in the selection, even though the mayor is likely to run for re-election in the Democratic primary this fall.

"I do not see it by any stretch of the imagination as a deciding factor. That won't be what decides it," the source said.

Some city hall observers were suprised with the lack of opposition to the mayor's swift appointment of Jefferson as the city's first black police chief, and believe that the relative calm with which that selection took place indicates that race has become a less explosive factor in such city appointments.

Another factor likely to be considered is residency, but here too the effect is not likely to be decisive. Some persons have complained for years about police chiefs who live outside the city. Lewis is a Washington resident. Devine lives in Clinton, Md.

Although 41 men technically are eligible for the job - city law forbids the election of someone not in the department as the new chief - there is a general feeling around city hall that only eight to 10 men are in the running.

Most of them are in the higher ranking positions. In addition to Devine and Lewis, there is John P. Breen, 56 of Landover, the former fire marshal who now runs the department's training division; and Deputy Chief Calvin Watson, 50, of the District of Columbia, who is in charge of the firefighting division. Breen is white; Watson is black.