Coming as it did from a high school senior, the question was a shocker. "Will Social Security be around when we get it?" the student asked the visiting congressman.

"Yes, very definitely," replied Rep. J. J. (Jake) Pickle (D-Tex.) almost reflexively. But then Pickle, who is chairman of the House subcommittee on Social Security, turned the question back on the students. How many of you think Social Security will exist when you retire? he asked.

Pickle was shocked again. Even though he had just assured them that Social Security will last forever, nearly half the students said they did not believe him. The seniors in this government class at Pflugerville High School reflect a deepening public cynicism about the Social Security system that may be far stronger than is generally believed.

Americans do not believe the political promises about Social Security, especially younger Americans who are paying in their contributions now through payroll deductions but do not believe the benefits will be around for them to collect when they retire.

According to a new Washington Post-ABC News opinion survey, an overwhelming number of citizens under the age of 45 think that Social Security will have disappeared by the time they are eligible to receive it. The poll, taken in late January, found that 66 percent of the respondents under 45 believe Social Security won't be there. Among those age 18 to 30, 74 percent are skeptical.

These poll findings, and the comments of other citizens interviewed in sample precincts, are striking because of the depth of cynicism about the reliability of a political commitment that was the heart and soul of the New Deal and has served the elderly for nearly 50 years.

Politicians in Washington have been reluctant to tamper with the basic provisions of Social Security, fearing instant political reprisal from the retired people who are recipients. But, if young and middle-aged citizens now believe that they will be eventually betrayed on Social Security's promises, that sentiment might push the debate toward enactment of long-range reform plans such as a phased reduction of benefit levels in order to insure the system's survival.

Interviews with citizens around the nation reveal an almost nonchalant fatalism about the future of this basic government guarantee. Bob Kulp grew up in Chicago and moved to Texas last year. He is in his mid-20s and works in the cleaning business. Sitting one morning in his home in Houston, he was asked whether he thought he would ever receive Social Security.

"No," Kulp said without hesitation. "I feel every dime I put in, I won't get back. I don't plan on seeing any of it."

There was no passion in his voice, no sense of outrage that the government would not make good its promise to provide him with a retirement income, just an acceptance of a new reality. "It doesn't bother me," he added. "It's just a way of life."

Karren Woolf, a Pomona, Calif., housewife, no longer expects to receive Social Security. "But we're investing money," she said recently, "and my husband has a profit-sharing thing at work, and we think that will be ample. But we do think it's a shame that we're putting this money into Social Security and won't get it back."

Kathy Hudak, who works for a brokerage firm in Texas, said: "I think it will be wiped out. We put into it, but I don't think we'll get it back."

The Social Security issue is so volatile politically that public officials won't even broach the subject of the system's demise. Most of them now take it as part of their job to reassure an increasingly skeptical public that government retirement benefits will be protected, seemingly at any price.

"Anybody who stops to think about it knows it's too important to the American people," Rep. Pickle said.

But in their own minds, many Americans are coming to the conclusion that the politicians are wrong, and no amount of official rhetoric from Washington seems likely to change that skepticism in the near future.

"I don't think my husband and I will ever see it," said a middle-aged woman who did not want to be identified. "I don't think my children will either. We're not planning on it anymore."

Ronda Hobbs of Houston shares that cynicism--and more. "I don't think it will exist"--when she retires--"but I think we'll pay in for 10 or 15 years and then it won't be there," she said. "You don't feel like you have any control over it at all."

Washington has done much to undermine the credibility in the system. Recurring "crises" in the Social Security trust fund balances have convinced some people there is no long-term solution to the program's solvency. Other people have been turned off by the continual sparring between the two political parties. Some believe that politicians are as interested in scoring points on one another as in restoring the system to financial health.

"Tip O'Neill wants it to die so he can beat Reagan over the head with it," said Mike Fry, a young political cartoonist in Austin.

The huge tax bill approved by Congress last year has coincidentally undermined confidence in Social Security. A young woman was in a midtown Manhattan bank in early January and found it almost like a carnival midway, with banners and signs urging customers to open up the new Individual Retirement Accounts that were authorized by Congress.

When she cynically commented to a middle-aged teller that the exhortation to set up IRAs was really just a ploy for preparing the public for the day Social Security collapses, the teller promptly agreed with her.

The aggressive competition for these new IRA accounts has prompted banks around the country to run newspaper and television ads warning the public that Social Security cannot provide for them in their old age. "Excuse me," says a man with a poor French accent in one ad running in New York. "Can you spare $5.15 for a cup of coffee?" This message has added to the public doubts.

The Post-ABC News poll differed from earlier attempts to measure public attitudes on Social Security in asking people bluntly: "There's been lots of discussion about the financial condition of the Social Security system. Do you think Social Security will exist or not when you retire?" The phrasing of the question is more provocative than many public opnion analysts would like but it reveals the full scope of curbstone skepticism.

"I don't think it will be there," said Becky Helmreich of Houston. "A long time ago I came to the opinion that it wouldn't be there."

Another woman, in her late 40s, initially said, "I hope to believe it will exist." She paused for a moment and then responded, "Not really."

The poll showed that there is a clear generational link to attitudes toward the future of Social Security. Those 18 to 30 years old are the most pessimistic, followed by those 31 to 44 years old. But a majority of respondents over the age of 45 express faith that the system would exist when they retire. Only 57 percent of those between 45 and 60 believe Social Security will last until their retirement age, compared with 82 percent of those older than 60.

Women are more pessimistic than men, with 64 percent of women saying the system will not survive, compared with 54 percent of men. Broken down racially, the poll showed that 64 percent of blacks have no faith in the future of the system, compared with 58 percent of whites.

The polling was conducted Jan. 22-30, which means half was done before President Reagan's State of the Union address and half afterward.

Of those interviewed before the speech, 58 percent said the system would not exist and 39 percent said it would, a difference of 19 points. After the speech, that margin grew to 27 points, with 61 percent saying they would not receive Social Security and 34 saying they would, suggesting at a minimum that citizens were not reassured by the president's remarks.

Social Security represents perhaps the most lasting promise ever made by the government to the people, and its originator, President Franklin D. Roosevelt, intended to make that compact as binding as possible.

"We put those payroll contributions there so as to give the contributors a legal, moral and political right to collect their pensions . . . ," Roosevelt once said. "With those taxes in there, no damn politician can ever scrap my Social Security program."

Most older Americans--and politicians of every age--still see the program as a legal and moral commitment, but the younger generation that matured on Vietnam and Watergate and saw other solemn promises abandoned is much more skeptical.

The attitude on Social Security may be only one part of an overall distrust of the federal government. Another question in the same Post-ABC poll suggests that younger Americans may be more cynical about other elements of American life that are taken for granted by older generations.

One precept of society is that if you work hard, eventually you will get ahead. Presented with that statement, respondents under the age of 45 are almost evenly split on whether they believe that is true, with 51 percent agreeing and 47 percent disagreeing. Those over 45, however, agreed by a 2-to-1 ratio.

In recent years, the evidence of skepticism about the future of Social Security has grown in proportion to publicity given to the system's financial problems. Congress enacted major payroll tax increases in 1977 in an attempt to shore up the system, but the weak economy already has overrun those changes.

A bipartisan committee is now studying the problem, and sometime next year there will be another major effort to restructure the system, which faces a shortage of funds in the mid-1980s and a long-term deficit of more than $1 trillion.

A CBS-New York Times poll taken last year found that 24 percent of respondents said they had no confidence in the system's ability to provide retirement benefits for them or their spouses, with another 49 percent saying they had only a little confidence.

The same poll showed that 75 percent of respondents between the ages of 25 and 34 said they doubted that the system would provide them with the full benefits to which they were entitled.

Twenty years ago, there were 5 workers for every Social Security recipient. Today there are 3.3 and by the year 2030, it is estimated there will be only 2. That means less revenue per recipient in the system or a greater burden on those of working age.

Compounding the problem is the added life expectancy of retirees. In 1940, the life expectancy of men aged 65 was 12.1 years, but today it is 14.3 years and by the turn of the century it is projected to be 16.4 years. Life expectancy for women has increased even more rapidly. That means retirees will draw money out of the system longer in the next century.

"It's already running out of money," said Tanya Fain of Austin. "By the time I get there, there won't be any money left."