Nobody would try to fly a plane with a right wing but no left wing.

Yet on national television, political discussion shows have just such an imbalance. No wonder those programs wobble so weirdly.

Take ABC's ''This Week with David Brinkley.'' Its pundit roundtable usually features rightist George Will along with establishment centrists Sam Donaldson and Cokie Roberts. No leftists need apply.

Now that ABC has hired conservative William Kristol as an on-air political analyst, the Brinkley show -- whose executive producer is Bush administration official Dorrance Smith -- tilts even further rightward. A couple of weeks ago, the Brinkley roundtable was made up of Kristol, Will and Roberts.

Why add Kristol to the panel? Why offer two rightists and no leftists?

Or should we pretend Cokie Roberts is a firebrand of the left? In the real world, she might sue for slander if you called her ''left-wing.'' The main ''cause'' she champions in Washington is the right of pundits to rake in big lecture fees from corporate interests.

But in the make-believe world of TV, Roberts is the kind of pro-corporate centrist who passes as a liberal, the only alternative offered to the fire-breathers of the right.

Network news executives and corporate sponsors seem to prefer TV debates that exclude half the political spectrum -- the half led by advocates for middle-class consumers, labor, the environment, minorities and others critical of the status quo.

As we go to press, CNN's ''Crossfire'' -- the verbal food fight for adults -- is looking for a new co-host ''on the left'' to take on conservatives like Robert Novak and John Sununu. That role has been played by the departing Michael Kinsley, a columnist and self-described moderate.

One of CNN's most-watched programs, ''Crossfire'' is the show that made a national TV star (and presidential candidate) out of its far-right co-host, Patrick Buchanan.

But ''Crossfire'' appears destined to remain as imbalanced as a one-winged airplane. The Los Angeles Times reported in late November that two ''strong candidates'' contending for Kinsley's job are Bob Beckel and Juan Williams.

Formerly a Democratic campaign operative, Beckel now heads a lobbying and consulting firm that represents corporate clients like the Walt Disney conglomerate, long-distance phone companies and insurance firms involved in the battle over toxic waste cleanup.

As a pundit, Beckel's views are often quite conservative. He consistently advises the Democratic Party to move rightward. In 1993, he hailed President Clinton's effort to downsize government as a great tactic to force a ''showdown'' with liberal Democrats, relishing that ''the unions will grumble, the left will scream.''

Beckel didn't just support the Gulf War; he denounced protesters as ''punks.'' Last year, he applauded Clinton for rebuffing liberals who urged greater cuts in Pentagon spending.

With such views, is Beckel an appropriate voice to represent ''the left''? In the real world, no. On TV, perfect.

The same could be said of Juan Williams, a Washington Post reporter. Search Williams' writings for his judgments on ''liberals'' or ''the left'' and you'll find more criticism than praise.

Williams starred in a historic ''Crossfire'' episode about the Clarence Thomas-Anita Hill clash. Substituting as the left co-host, Williams was supposed to be a counterweight to Pat Buchanan, who wailed that liberal conspirators were persecuting Thomas. But Williams agreed with Buchanan.

Two days later, it looked like Buchanan had written Williams' column, attacking ''so-called champions of fairness: liberal politicians, unions, civil rights groups and women's organizations.'' The column concluded that ''liberals have become monsters.''

In recent weeks, the center-to-right TV pundit brigade has been expending surpluses of hot air about the budget. But we rarely hear calls for cuts in military spending. Or increased taxes on the wealthy. Or raising the corporate income tax -- which accounted for 25 percent of federal expenditures in the 1960s but only 14 percent now.

Outside of Washington TV studios -- in the real world of grassroots politics, union halls, churches and college campuses -- such proposals make sense to a lot of people.

In the real world, of course, airplanes with just one wing don't fly.