A group of Fairfax County senior citizens yesterday helped Republican Frank Wolf place his Democratic congressional opponent Rep. Joseph L. Fisher on the defensive during a spirited debate in McLean.

Aided by pointed questions from a gathering of 100 members of the McLean chapter of the American Association of Retired Persons, Wolf clashed with Fisher over gun controls, voting representation for the District of Columbia, the Panama Canal treaties and whether federal workers should be covered by Social Security.

Fisher, a two-term incumbent, said he favored controls on cheap handguns, so-called Saturday night specials, adding: "I'm very leery of laying on gun control, gun registration and licensing laws." Wolf, a former Interior Department liaison man on Capitol Hill, opposed any gun controls. "It has not worked." he said of gun control legislation.

One questioner asked Fisher how he could justify his vote in favor of allowing the District of Columbia full voting representation in Congress in view of the relatively small number of voters in Washington's recent elections.

The congressman said he was "sorry" so few of the eligible voters in the city voted and said. "I'm worried now that there will be an equally low voter turnout in this election" in the 10th Congressional District.

Wolf who opposes voting representation for Washington said the city's representatives in Congress would push for a commuter tax. "If there is a commuter tax, we in the state of Virginia, will lose $76 million," Wolf said.

The audience broke into applause when Wolf told them he would be opposed to the recently passed Panama Canal treaties, if the issue ever came before the Hosue of Representatives. Fisher said approval of the treaties was a matter handled by the Senate. "I do not think it would be in the best interest for the House . . . to try to thwart the constitutional decision that the Senate has made," the congressman said.

Fisher said he would favor a two-year study on whether a plan can be devised to place federal workers under social security. Wolf said he opposes proposals to place any current federal workers under social security, but he would favor placing people who join civil service after 1980 or 1982 under it.