More than two-fifths of American workers have "hardly any confidence at all" that the Social Security system will be able to pay them the benefits they've earned, according to a nationwide Lou Harris poll.

Another two-fifths have "less than full confidence" that the system will be able to deliver future benefits.

This startling reflection of doubt about Social Security's financial condition was one of the major findings of an August 1978 Harris poll of 1,330 workers, 369 retirees and 212 companies that was disclosed yesterday at a hearing before the House Committee on Aging. The poll was conducted for the pension firm of Johnson and Higgins.

In a statement later on the poll, Stanford Ross, commissioner of Social Security, said, "There is no doubt that American workers will get the Social Security benefits to which they are entitled. In the final analysis, the federal government, reflecting the American people, stands behing the promise to pay."

Meanwhile, Ross told reporters he is starting a campaign to clean up Social Security earnings records because about $69 billion in wages earned by workers since Social Security taxes started 42 years ago has not been credited to their accounts.

Ross said the $69 billion represents only a tiny fraction (0.7 of 1 percent) of the $9.7 trillion in Social Security-taxable wages earned by workers since 1937. About half of the $69 billion was earned before 1955.

He said it is the Social Security Administration's responsibility to correctly credit all workers. Persons who feel their wage records have been lost or improperly posted should contact Social Security, he added.

Ross said failure to credit taxed earnings to a worker's account normally results from incorrect names or Social Security numbers supplied by an employer. With its computers, Social Security catches most of the earrors, but records now show $69 billion in earnings under names and numbers it cannot link to anyone.

"Usually these incorrect wage reports are for short-term and transient labor, such as restaurant workers or car-wash employes," Ross said.

Ross said it is unlikely many workers would lose substantial benefits. Some of the persons involved are probably a already dead, he said; others will catch the error when they apply for benefits and can provide personal information about where they have worked. Still others will not be affected because lost records involve low-earnings years which often are "dropped out" of benefit calculations, by law.

Although fear about the financial soundness of Social Security was the most striking Harris finding, the survey covered a wide range of retirement and pension issues. These included:

About half of all employes said they would prefer to work full or part time after reaching retirement age, rather than retiring.

The most important characteristic of pension plans, other than the basic level of benefits, was the need for automatic cost-of-living increases to counter inflation. Two-thirds of those surveyed called it "extremely important" and another 27 percent "very important." (Social Security and civil service pensions have automatic cost-of-living increases compared with 3 percent of private pensions.) Inflation is "clearly the No. 1 problem facing retirees" and 40 percent say it has "seriously" reduced their standard of living. Another 40 percent say it has hurt them "to some degree."

Eighty percent of employes believe employers should be required by law to supplement Social Security with a private pension, but employers opposed such a law 2 to 1.

Two-thirds or more of employes would be willing to contribute more toward pensions if it increased benefits and ensured cost-of-living increases. Most employers said private pensions should be financed solely by the company.

Three-fourths of current and retired employes are satisfied to have Social Security provide only a basic level of income -- to be supplemented by private pensions and savings -- largely because they doubt the government's ability to manage a higher-benefit program that would eliminate the need for private pensions.

Sixth-six percent of business leaders surveyed felt pensions should be imvested for the highest return, regardless of a company's or country's social policies.