July 1, 1983

The Nuclear Regulatory Commission said yesterday that, in principle, the Shoreham reactor on Long Island could be allowed to load fuel for low-power testing, even though it may never be permitted to operate commercially. The commission did not give the operator, the Long Island Lighting Company, permission to load the nuclear fuel, but its 3-to-2 vote cleared away a major obstacle. The commission acted after a threejudge licensing board, which has been hearing the Shoreham case, said that uranium should not be loaded before there was ''reasonable assurance'' that a dispute over emergency planning would be resolved and full operation allowed.

The third and final stage of President Reagan's income tax cut, the keystone of his economic program, takes effect today, and is expected to save taxpayers $30 billion over the next 12 months. Many economists believe the tax cut will stimulate consumer spending and an economic recovery in the second half of 1983. (Page A1.) Mr. Reagan has delivered both personal income tax reductions and an improving economy, but they follow a severe recession. (B9.) Bank regulators decided to eliminate all remaining interest rate ceilings on savings certificates purchased after Oct. 1, and to ask Congress to permit banks and thrift institutions to pay interest on checking accounts held by businesses. The decision eliminates interest rate limits on the popular six-month savings certificate. (D1.)

Norton Simon Inc., the big consumer products company, has accepted a sweetened takeover bid from Esmark Inc. estimated at $918 million, the companies announced last night. The announcement, telling of a definitive agreement, followed marathon negotiations Wednesday and yesterday between David Mahoney, chairman of Norton Simon, and Donald P. Kelly, chairman of Esmark, a food processor and manufacturer. Esmark's new two-step bid was valued at an average price of $34 a share in cash and stock, up $1.75 a share from its earlier proposal. Wall Street analysts said they expected the deal to go through, although there was always a possibility that other suitors might yet outbid Esmark.

The first half of 1983 was a time of plenty on Wall Street, with the vast majority of stocks surging upward in a continuation of the powerful bull market that began last summer. But even in a bull market, there are losers. While most investors were making their fortunes, an unlucky few lost a lot of money. The biggest winner on the New York Stock Exchange so far this year has been the International Rectifier Corporation of Los Angeles, a little-known maker of semiconductors and pharmaceuticals that recently invented an inexpensive, highly efficient technique to power silicon chips and other electronic devices.

Mayor Koch announced yesterday that he was abandoning his policy of trying to collect property taxes from many cultural and other nonprofit organizations. The Mayor said he had decided that the path of ''good sense'' required him to make it easier, not harder, for as many as 300 such groups to gain tax exemptions. He said he would propose legislation to the City Council that would allow those groups to qualify for exemptions as ''educational'' or ''charitable'' institutions. The organizations that would benefit range from large museums and foundations to tiny storefront organizations that serve ethnic and racial groups.