Alexandria's Democratic mayor and all three Democratic City Council incumbents are to kick off a joint campaign today after deciding that selling a solid front is the best way to get reelected in May.

"It's an effort to avoid a lot of expense and backbiting during the primary," said three-term Democratic council member Donald C. Casey. He is to join Mayor Charles E. Beatley, Vice Mayor Patricia S. Ticer and council member Lionel R. Hope at the city's first official 1985 campaign event at 5 p.m. in the Alexandria Community Y, 418 S. Washington St.

Party workers will begin circulating brochures with all four Democrats listed as a slate this evening, and all campaign donations will be divided equally unless earmarked for a certain candidate, Ticer said.

"There is a fraternal feeling among us, so we decided to board the same ship," said Beatley, agreeing that the joint campaign effort was an uncommon procedure.

Beatley, seeking his sixth term as mayor, said he could not recall in two decades an election similar to this one in which no vacant council seats were at stake. All seven incumbents -- including three Republicans -- are expected to file for reelection by the Friday deadline.

Both the Republicans and Democrats will hold primaries on March 5 if more than six candidates in each party contest the election scheduled for May 5. So far, council member Margaret B. Inman is the only Republican to have officially filed for the race.

Along with the four Democratic incumbents, two other Democrats already have filed: former council aide Del Pepper and former congressional candidate Craig Coverdale.

Casey, a lawyer and one of the most outspoken council members, said the timing of the current city-ordered investigation into allegations of misconduct by three top Alexandria officials added another reason for showing the public "that the majority of the council is stable and can work together."

He called the timing of the probe "dreadfully poor."

The investigation, conducted by Washington lawyer Abbe D. Lowell, centers on allegations that Director of Public Safety Charles T. Strobel prematurely called off a police drug investigation earlier this year after the names of two city officials were mentioned in a recording made by a police undercover agent.

In addition to Strobel, the council unanimously voted that City Manager Douglas Harman, Strobel's superior, and Alexandria Sheriff Michael E. Norris be investigated.

Ticer, a PTA activist and real estate agent who became vice mayor earlier this year after James P. Moran resigned the office, estimated that each Democratic incumbent will spend between $12,000 and $15,000 on the campaign.

Moran, an Alexandria stockbroker, resigned in June after pleading no contest to a misdemeanor conflict-of-interest charge based on findings by a special prosecutor that he had a business relationship with a developer who was trying to negotiate a land deal with the city. Moran is expected to throw his hat in the council ring again, and said Friday he will announce his final decision next Friday. He said if he does run, he'll ask the four Democratic incumbents if he may join their slate. "If even one member is embarrassed or resentful that I am running, I won't join the team," he said.

Casey, who had sharp words with Moran over the conflict-of-interest charge that led to Moran's resignation, said he had no problem with any other Democrats "tagging along" if they wished. "What we are looking for is a Democratic sweep," he said.

Robert Calhoun, one of the three Republican council members, called the Democrats' joint effort "a new campaign tactic that will be difficult to follow through on."

Calhoun, who in 1982 became the city's first Republican mayoral candidate since Reconstruction, said the Republicans have been holding off announcing their reelection plans to give new Republican candidates "a chance to get some visibility."

Calhoun already has circulated petitions pushing his candidacy for both mayor and a council seat next year. He said he will announce which office he will seek after the new year.

He added: "If I thought there was going to be any sort of a Democratic sweep, I'd tell you right now that I quit."