Northern Virginia congressional candidate Ira M. Lechner yesterday charged that his Republican opponent, Rep. Frank R. Wolf, "reneged on promises he made as a candidate" two years ago and twice voted against cost-of-living adjustments for the more than 23,000 federal and military retirees who live in his district.

"The record shows broken promises and broken dreams," the 48-year-old former Democratic state delegate from Arlington told a generally friendly crowd of more than 500 who had come to a Falls Church high school auditorium for the debate sponsored by the National Association of Retired Federal Employees.

Wolf, whose district contains more active and retired federal workers than any in the country, defended his record, saying he has worked "hard and very effectively in a very difficult fiscal and political environment."

"I have done as much as humanly possible," said Wolf, 43, who told the group he frequently has defended the interests of federal workers before hostile congressional colleagues. "I think you should vote for me because I've been a very effective congressman. I've been very efffective in protecting cost-of-living adjustments."

Lechner attacked Wolf's record, reading from Wolf's 1980 campaign literature in which Wolf promised to keep intact semiannual pension adjustments. In l981, Lechner said, Wolf voted for a Reagan budget package that called for annual increases.

"I think you deserve a champion," said Lechner, who added that last May Wolf voted for a budget resolution proposed by Rep. John H. Rousselot (R-Calif.) that would have eliminated 1983 cost-of-living increases for federal employes. "What message did that send to the rest of Congress?"

Wolf did not explain his vote on that resolution yesterday. He said recently that he had voted for it as a "symbolic gesture" because he knew that it stood no chance of passing.

"I care, I care, I really care," said Wolf, who told the group he had sponsored a senior citizens conference and recently secured a one-year extension of federal employe health benefits to cover care in the Hospice of Northern Virginia, a facility for terminally ill cancer patients.

"My father was going through the same process, dying of cancer," he said in the first of two references to the recent death of his father, a retired Philadelphia policeman.

Referring to Lechner's often-stated exhortation that voters make the race a referendum on Reaganomics, Wolf said: "Such an action would have the opposite effect. I have been able to persuade the administration to support federal workers . . . . My opponent's election would put fear in the heart of no one in Washington."

Several hours before the debate, Lechner completed a four-day, 55-mile walk across the district, meeting some 100 supporters in the parking lot of Arlington Cemetery. The group then walked the 1.7 miles across Memorial Bridge and into Washington for a rally outside the Office of Personnel Management, featuring Maryland Democratic Rep. Michael D. Barnes.

"We want to show federal workers that we'll walk the extra mile for them," said Lechner, who wore grey suede running shoes and sported a gold neck chain, a gift from campaign workers.

"I'm very proud of what Ira's doing," said Barnes, who arrived 15 minutes after Lechner. Barnes said that Wolf "has voted consistently against the federal employes of this country, the senior citizens, the elderly, the handicapped. Yet he says I was for [reducing cost-of-living adjustments] . . . but it was part of the budget package. . . . I voted for the package, but I wasn't for what was in it."