Nearly a quarter of the nation's insurance companies are in potential financial difficulty, about double the number in that position four years ago, according to insurance regulators.

The National Association of Insurance Commissioners, which prepares an annual "watch list," told a congressional panel that of 2,127 property/casualty companies whose 1986 financial records were examined, 513 or 24.1 percent were judged to be needing immediate regulatory attention or to be targeted for future scrutiny. The first category indicates the company is in danger of insolvency while the second signals potential long-term financial problems. The 1986 figure for the life and health insurers is 21 percent.

Despite the property/casualty industry having enjoyed record profits last year, the number on the watch list is comparable to 1985's 23 percent. Poor underwriting practices of several years ago, prompted by a rate war, are still showing up in claims. In 1983, by comparison, 11.5 percent of property/casualty companies were perceived by NAIC to have possible financial troubles.

"These figures are truly alarming," said Nick A. Verreos, president of the National Association of Professional Insurance Agents. "They expose an industry still paying the consequences of its feast-or-famine markets, which has tested the limits of both consumers and Congress and demonstrates the need for tougher state oversight."

Not all carriers on the watch list become insolvent. This year, regulators have closed 10 interstate companies versus 22 last year and 23 in 1985, according to NAIC.

However, as alarming as the property/casualty company figures are, they pale beside the long-term threat faced by the life and health insurance companies, which must deal with the growing epidemic of acquired immune deficiency syndrome, said Michael A. Hatch, commissioner of commerce and a member of NAIC

Current figures for these firms are less grim than for property/casualty. For 1,654 life and health companies, the potential trouble rate is 21 percent in 1986 -- but shows a 4 percentage point increase over 1985 figures. Four life and health companies failed in the first half of this year, compared with five in 1986 and two the previous year.

But the looming burden of life and health claims from AIDS victims clouds the industry's future, NAIC said, and must be considered along with other concerns, such as undercapitalized health maintenance organizations, potential capacity problems in the annuity business, and junk bonds purchased as investments by insurance companies.

All states have guaranty funds that are supposed to protect policyholders in case of property/casualty carrier failures. However, 13 states are without similar funds for life and health companies, according to NAIC.

Five state insurance regulators testified yesterday before the House subcommittee on commerce, consumer protection and competitiveness, which is examining the possibility of federal legislation to deal with the liability crisis and other insurance problems.

The only area in which the regulators agreed to federal legislation was product liability insurance because they said uniformity of liability limits is desirable when products are sold interstate. There was no consensus among state officials on other important questions, such as whether the federal government should be involved in pollution or AIDS insurance, international reinsurance or state guaranty funds.