When Ronald E. Fuller joined the Alexandria Fire Department 29 years ago, he had not intended to make his first assignment as a fire dispatcher his career, which it turned out to be. And until last week the crusty 57-year-old said he had no second thoughts about his decision to be a city servant.

That's when Fuller and the rest of Alexandria's more than 400 public safety employes learned of a City Hall plan that calls for a radical reorganization of the city police and fire fighters' liberal pension plan that, because of high costs to maintain, is viewed as potentially ruinous to the city.

The plan outlines cuts in disability benefits and yearly cost-of-living raises to some workers and more and tougher eligibility requirements to qualify for benefits, and it has shocked the public safety employes, who usually shy away from confrontation with City Hall.

Fuller, a soft-spoken man, was quick to express his outrage: "I've been a faithful worker and paid my part into this pension," he said yesterday. "Now I feel the city should do the same--be faithful to its committment."

A report by a bipartisan City Council subcommittee concludes that the 27-year-old pension plan has been abused and therefore must be overhauled. Last night both sides met to discuss their differences over the plan, which the Council is considered likely to adopt when it votes on the city's 1983-84 budget Monday.

"I expect a court battle," said Vice Mayor James P. Moran Jr., who, with fellow Democratic council member Lionel R. Hope and Republican Carlyle C. Ring Jr., make up the pension subcommittee.

Attorney Richard Wohltman, representing the police and fire fighters, said it is likely that the public safety employes will sue the city to block adoption of the plan if issues aren't resolved through negotiations.

Moran said yesterday he is confident that the council is willing to modify some of the details of the plan, but the basic premise must remain the same: "We've had too liberal a plan that too many people have taken advantage of. So we are now confronting a situation that has gotten out of hand."

City officials said taxpayers contributed more than $4.42 million to the pension program last year, and $3.8 million the year before.

According to the report, in 1972 the average police and fire fighter retired at age 58. None retired on disability that year. Eight years later, the average age had dropped to an all time low of 50, and 10 retired on disability. Currently, 72 former workers are collecting lifetime disability payments.

In some cases, the report found, workers who retired on disability could make more money than if they had stayed on the active payroll.

A 1982 study by the Connecticut General Life Insurance Co., which operates the pension fund, said the city faces more than $30 million in unfunded disability liabilities because of the number of workers retiring under the plan.

"Because of loopholes in the old plan, the city feels many took advantage of it," said council member Hope. "If we continue under the old plan, what will happen is we will wreck the city" financially.

The proposed changes call for, among other things, reducing the benefits for future partial disablity retirements from 66.5 percent of a worker's final earnings to 50 percent and abolishing cost-of-living raises for some workers.

Alexandria police Sgt. Bruce R. Pray, spokesman for the 200-member city Police Association, said the report distorts reality. He said the pension plan is financially unsound because the city had consistantly underfunded it in recent years, which the city acknowledges.

Pray added that no city official has been able to document one case of abuse of the retirement program, to which public safety workers contribute 8 percent of their annual salaries.