Labor Department pension benefits chief Ian Lanoff said yesterday that the number of persons receiving private pensions in the U.S. - 7 million - is "horrifyingly small," and leaves a large portion of the 24 million aged persons in the country without adequate income.

Lanoff told a retirement conference organized by the Pension Rights Center, "The first order of business is to expand private pension coverage."

Only half the labor force is working in jobs that may someday produce pensions, he said. Many will never vest in any pension because people change jobs so often. Benefits aren't portable when you move from one job to another. And many who meet all eligibility criteria will never receive a cent because the law, in effect, lets some forms set up plans that pay benefits only if your wages exceed the Social Security tax write off.

"The pension reform act's current protections are inadequate for insuring decent retirement incomes for women," Lanoff said, because many women work only part-time or intermittently, making it even harder for them than for men to meet 10-year vesting requirements.

Moreover, in some cases, if a fully vested worker dies before he has started taking his pension, his widow may end up with nothing.

Sen, Howard Metzenbaum (D-Ohio), another speaker, said private pension managers are contributing to the decline of the Northeast and Midwest by pouring billions of pension investment dollars into firms that use the money to build plants in the union-free Sunbelt or overseas.

"If they live and work in the industrial Northeast and Midwest," Metzenbaum charged, "they (workers) will learn that money that could be used to make sound investments in their region is flowing to investments in low-wage foreign countries."

Metzenbaum said that, "In the long run, those investments may destroy the livelihood of the people for whom they allegedly are being made.

"If these contributors are union members, they will learn that their money is being used to create a 'union-free environment' in the so-called Sun Belt."

Metzenbaum said the reason pension funds can be used this way is that there is tremendous concentration in management of the pension trust funds. He said that at present, state and local government and private pension funds total about $500 billion, which will grown to $1 trillion in seven years and "make up almost half the external capital raised by U.S. corporations." However, he said, a relative handful of banks and insurance companies manage the money.

"At the end of 1977, the top 10 banks controlled nearly $75 billion in pension funds. Prudential Insurance, Equitable Life and Morgan Guaranty each controlled $15 billion.

Although these institutions are supposed to have financial expertise, the charged, theirrecord on investment return had been "positively embarrassing." From 1962 to 1978, he said, 37 percent of all pension fund managers failed to keep pace in the pension investments with stock market performance in general, as measured by Standard and Poor's 500-stock index.

Metzenbaum said it is universally accepted that pension managers should try to invest the money in a way that keeps it secure and produces a good return, but there is no reason they shouldn't invest it closer to home in many cases, avoiding subsidizing overseas and Sun Belt competition.

He noted that unions like the Amalgamated Clothing and Textile Workers and International Association of Machinists had served notice that they will demand some say over how funds held for their members' pensions are used, and that Citibank, one of the biggest pension managers, had been inviting the ultimate owners of stock which they held for pension funds to participate in decisions how to vote that stock.

Prof. Roy Schotland of Georgetown agreed with some of Metzenbaum's statements but said a pension manager shouldn't go overboard on social-responsibility investments because "the primary purpose" of the manager is to protect and enhance the money.