Private pension funds have more than $300 billion in assets, making them one of America's largest pools of capital. When the economy turns sour and high interest rates make raising cash very expensive, the temptation to companies is to draw funds from that pool and apply them to corporate uses, despite the existence of laws to protect private pensions.

The Internal Revenue Service reports an increase in the number of companies requesting permission to defer payment of pension contributions. During a seven month period ending April 30, 1982, there were 310 such requests, representing an increase of 36 percent over the 228 applications made in the same period the previous year. Waiver approvals rose by 16 percent in the same period, to 202.

The IRS grants such requests only when it finds sufficient evidence that the business is "unable to satisfy the minimum funding standard for a plan year without substantial business hardship and that making contributions would be adverse to the interest of plan participants in the aggregate."

Moreover, companies are not only declining to pay what they owe into pension funds, they also are taking back what they have already paid in some cases, again with the approval of the federal government. The Labor Department reports that the number of loan or credit arrangements between pension or profit sharing plans and employers grew to 25 in 1981 from just one in 1975. In the first six months of this year, 25 such arrangements have been approved.

In other words, sometimes it becomes a choice of saving the pension plan or saving the sponsor. With IRS approval, Braniff International ceased making contributions to its defined benefits pension plan in 1980 or about the time its expansion spree ran into turbulence. Monies that would have gone for retirement went for jet fuel when the price doubled. By the time it filed for reorganization in bankruptcy this year the fund's liabilities exceeded assets by over $150 million, according to Securities and Exchange Commission documents.

International Harvester Co. totters on the brink of bankruptcy. In an effort to raise cash, management recently took the bold step of selling all of its pension fund's $250 million stock portfolio and replacing it with bonds, a move that is calculated to save it an estimated $50 million a year in annual pension contributions. It is a calculated gamble to lock in interest rates; it could succeed in doubling the fund's assumed interest rate of 7 percent or build up its unfunded liabilities if the bond market again founders. Alicia H. Munnell, a pension expert who is vice president of the Federal Reserve Bank of Boston, recently calculated that International Harvester had $1.1 billion in unfunded liabilities, the second largest of any U.S. company, following Chrysler.

The Pension Benefit Guaranty Corp., the government-chartered corporation that insures defined benefit pension plans, expects to be stuck with $60 million to $70 million of the Braniff liabilities, the largest single claim ever on PBGC. Should International Harvester go under, PBGC's liability would be about half a billion dollars.

Claude Pepper (D-Fla.), chairman of a House select committee that tries to protect people's pensions, has warned that if there is one more bankruptcy the size of Braniff, the insurer itself could go bankrupt. PBGC insures not only pensions of bankrupt companies, but also those plans abandoned by still solvent companies. As such, it has already assumed pension liabilities that exceed its assets by $180 million, a figure that is expected to rise to $236 million by the end of 1982.

In the past, 96 percent of all terminated plans had enough assets to pay their obligations, but if bankruptcies continue at the present rate of 80 per 10,000 companies, or 75,000 a year, more funds will be broke. PBGC is empowered to collect up to 30 percent of a company's net worth to offset a terminating plan's liabilities. In reality, bankrupts often have little net worth. So PBGC Executive Director Edwin M. Jones says that the government insurer will "give full consideration" to arranging involuntary terminations of plans in the future before bankruptcy occurs in an effort to salvage some net worth. Other pension experts suggest changing the law to give PBGC a claim to 30 percent of a company's assets or making it 100 percent responsible for pension liabilities.

PBGC's immediate solution to its financial problems is a request to Congress to raise its annual insurance premiums paid by employers from $2.60 per worker covered to $6. Jones admits the proposed premium does not take into account the current wave of bankruptcies that could make it necessary to raise the level even higher. An International Harvester failure, for example, would hike the premium to $9. This is a Catch 22 situation: the more premiums increase, the more companies will elect to drop their pensions and the less workers will be protected.

PBGC was one of the safeguards created by the Employee Retirement Income Security Act of 1974. Notwithstanding, there was dramatic testimony before Pepper's committee recently showing how hard times and loopholes in the law have combined to cause some workers to lose benefits without any bankruptcy occurring. He declared, "The management of these employers have apparently been tempted to treat these pension trusts like their own personal piggy banks, greedily breaking into them, and raiding them on that rainy day of their own financial difficulty."

In one case, the action was taken with the concurrence of PBGC. William Walsh, a retired executive of the Great Atlantic and Pacific Tea Co., described events leading to a class action by pension plan beneficiaries against A&P. He accused the financially troubled grocery chain of diverting a surplus of $250 million last October from the employes' pension fund to corporate uses. He alleged that the sum gained through the seizure of assets equals the amount originally put up by Erivan Haub to buy the company in 1979 through the West German corporation, Tenglemann Inc.

Although the new owners did not contribute to A&P's pension fund, the fund grew to more than $200 million by 1981. Without informing pension plan members, the board last June changed its rule that excess assets would be distributed to those members if the plan were terminated. Four months later it terminated the plan, affecting 26,000 people, Walsh said.

Walsh contended that the assets were not really "excess" because A&P had used too conservative actuarial assumptions over the years. Moreover, he said A&P's retrenchment, resulting in the closing of many stores and furloughing of many employes, had left A&P flush. It had $55.6 million in cash and short-term investments at the end of 1981, he said.

Walsh has filed a class action suit against his former employer. A&P recently offered to settle out of court for $50 million plus legal expenses.

Also suing his former company is Raymond C. Harwood, retired chairman of the New York publisher Harper & Row. Last year, the current management terminated its pension plans to realize $11.3 million as part of $20.4 million needed to buy a third of its own stock, which was being sold by the Minneapolis Star & Tribune.

Harper agreed to pay $20 a share for the stock, or twice its trading price in the over-the-counter market. Since then the stock, which was valued at $13 a share when it went into the pension fund, has dipped to 8 1/2, meaning a paper loss of $3 million to $4 million for beneficiaries.

In a separate suit, the company union contends that Harper created "excess" assets by actuarial maneuvering so that its plans were overfunded when they were terminated. Employes who received lump sum payments got much less than the fair actuarial equivalent of their benefits because the company used a 15 percent interest rate assumption, double the rate the union says it should have used.

Harwood stressed that although Harper may have had the legal right to do so, it did not have the moral right to deprive plan beneficiaries of these monies. He added that the action and the establishment of an employe stock ownership plan in place of the pension and profit-sharing funds had weakened morale at the company.

But a Harper spokesman responded that as a result of the stock purchase, the company would remain independent, and employes "will now be able to participate in a meaningful way in the success of Harper & Row, bolstered by a tremendous new incentive for productivity and growth."

Pepper has proposed legislation to make private pensions universal. In the current economic and regulatory climate, the idea appears to have little support. A more plausible alternative, experts say, is a change in pension law to strengthen PBGC and thereby increase protection for plan participants. Among the ways experts suggest this could be done are to establish a risk-related insurance system so that well-funded companies would not have to foot the bill for ailing pension systems.

Corporations should be prevented from spinning off subsidiaries with underfunded plans, as International Harvester did with Wisconsin Steel to escape its termination liability. Finally, it is suggested that insolvency be made the insurable event rather than plan termination. That would help PBGC cut down the costs of administering 659 defunct plans, which now amount to 89 cents for every $1 paid out.