The House Ways and Means Committee yesterday tentatively approved tax credits to industry and businesses that try to save energy.

The committee approved, 12 to 5, a plan for rebating the tax imposed on industries and utilities that use oil or natural gas if they convert to coal, a more abundant fuel source. They could take either a dollar-for-dollar tax rebate, up to 100 per cent of the tax, to apply against conversion costs, or an additional 10 per cent investment tax credit on top of the existing 10 per cent investment credit.

The administration estimates that the tax would raise $44 billion by 1985 and that about $34 billion of that would be rebated under the plan. This carrot-and-stick program is expected to be the biggest oil saver in President Carter's energy program. Administration officials hope it would save between 2 1/2 and 3 million barrels a day of or its equivalent in natural gas.

In a related action, the committee voted. 13 to 7. to give a special 10 per cent investment credit to businesses not benefitting from the coal conversion credit if they install energy saving equipment such as insulation and co-generation equipment, which uses wasted heat.

Meanwhile, a House Government operations Committee approved another piece of Carter's energy package. The proposal would encourage vanpooling by authorizing the government to buy up to 6,000 10-passenger or larger vans to carry federal employees to and from work. The idea is to encourage king-size car pools to get workers to and from the job at less cost in money, energy and parking.