The nation faces the prospect of a "generational war" that pits young against old unless Social Security benefits are adequately funded, a member of the President's Social Security Advisory Commission warned here today.

"Our problem is not just the senior citizens who want their checks every month, but the young people who are paying for those checks and who want to know there will be something left for them," said Rep. Barber B. Conable Jr. (R-N.Y.), a commission member and the ranking Republican on the House Ways and Means Committee.

Conable, former Social Security commissioner Robert M. Ball, also a commission member, and others both praised and picked apart a compromise Social Security rescue plan designed to provide $169 billion to the system over the next seven years.

Appearing at a day-long public forum on Social Security's future sponsored by the University of Maryland-Baltimore County, speakers outlined the commission's rescue package and answered questions from an audience of 100.

They also spotlighted some of the opposition the report faces, particularly its recommendations to delay cost of living increases by six months, tax Social Security benefits for upper-income recipients, increase the tax on the self-employed and extend mandatory coverage to new federal workers and employes of nonprofit organizations.

"Everyone has a vested interest in the way things are and feels change will be to their detriment," said Conable, referring to labor, business, federal worker and retiree groups who have attacked various commission proposals and who were represented at the meeting.

About 116 million workers, roughly half of the U.S. population, now pay Social Security taxes that fund benefits to about 36 million retired or disabled workers and their dependents or survivors. The system took in about $203 billion in fiscal 1982 and paid out about $206 billion. The shortfall is expected to grow worse as the number of retirees increases.

Defending the commission's recommendations, Conable said the report was a compromise on a complex, volatile issue that needs to be dealt with soon.

"The longer it gets poked at, the more likely it is to become unraveled, and we'll have a generational war, with young people refusing to support the funding system," he said.

Ball, however, downplayed the funding shortfall, saying modest adjustments in revenues and benefits would correct it.

"The dire picture of the sky falling down isn't so, has never been so," Ball said.

But he, too, defended the compromise report as the outcome of negotiations that "hung by a thread time after time."

The maneuvering was so delicate, he said, "that this has to either stand or fall as a package--which doesn't mean it can't be changed around the edges."

Troubled by more than the proposal's edges was Nick Staffa, a 66-year-old member of a retirees' chapter of United Auto Workers.

He objected to the cost-of-living delay and the tax on benefits. But he was all for having the system cover everybody.

"If I was forced into it, everybody should have been forced into it," he said.