In a flurry of activity last week, accounting rule makers announced plans to set new standards that may cost individuals and industry billions of dollars.

The Financial Accounting Standards Board, an organization that sets rules for financial reporting at publicly held companies, sent out two "statements" advising companies and accountants of upcoming changes this week.

One change will force companies to set up reserves for their employees' post-retirement medical benefits instead of paying these benefits out of current earnings, which is the general industry practice.

Some industry experts have said that if corporations did nothing to restrict their costs (that is, cut back on employee benefits), this rule could cut into corporate profits by as much as $200 billion over a period of years.

The other rule is designed to give shareholders more current information about company-held investment portfolios. But company insiders and analysts say that it will force financial institutions to spend millions of dollars hiring legions of actuaries and accountants to do nothing but comply with the proposed rule.

Neither rule will go into effect immediately. The medical benefit rule, for example, starts in 1993. And the other could be delayed even longer.

But already companies and their consultants are scrambling -- trying to change their operations in ways that will make these rules less costly.

"This will have a significant impact on companies, their financial results and their employees," said Marsha Venturi, consulting actuary with Buck Consultants in Secaucus, N.J., about the retirement benefit rule. "When companies take a good look at how expensive those benefits are, they are going to start reevaluating what they provide."

Venturi said that several of her clients have already changed benefit programs to limit their future expenses. Some are requiring retirees to ante up more per month for their own insurance, others are capping company-paid benefits and others are making working employees contribute more to pay for benefits they may collect when they retire.

In short, companies may find their earnings hit by the rule, but employees will feel the pinch, too, Venturi said.

Meanwhile, financial services companies are still trying to fight a proposed rule that would force them to disclose the current market value of their loans and investment portfolios in the footnotes of their financial statements.

Although these footnotes generally are read only by accountants, financial analysts and reporters, some say that calculating the figure will require legions of accountants and actuaries.

The rules would apply to all companies, but banks, savings and loans and insurance companies would be most affected because they often hold large portfolios of loans and investments. These assets are generally recorded on their books at their original purchase prices. The accounting rule makers want companies to say what the assets would be worth if they had to sell them today.

"This will cost millions. Serious millions," said Joyce Culbert, vice president of research at Firemark Insurance Research in Parsippany, N.J.

"Insurance companies would have to have appraisers on staff to reevaluate every {shopping} mall. And you'd need another horde of actuaries to figure out the present value of your insurance policies," she said. "This would be exceptionally costly."

Nevertheless, many industry observers are in favor of the new rules because they say that they will give investors a better picture of a company's true financial health.

Post-retirement benefits can be a huge liability. And if it is not disclosed, investors could be blindsided when a company is forced to start paying these benefits from current earnings.

Moreover, financial services regulators have been widely criticized for allowing "once upon a time" accounting of investment portfolios. Accounting standards that did not require up-to-the-minute disclosure of what assets were worth was cited as a major problem in the savings and loan debacle.

Some experts maintain that regulators simply did not know how sick some thrifts had become because accounting rules did not force them to disclose when their investments had soured.