Fifteen months ago President Carter sent to Congress as his most important legislative request a package of more than 100 proposals to reduce costly reliance on foreign oil by saving the equivalent of 4.5 million barrels a day by 1985.

By use of both carrots and sticks - taxes, tax credits and regulations - Carter planned to reduce use of oil by raising its price and move the nation toward other sources of energy.

The centerpiece of the program, on which the administration said all else depended, was to be a tax on domestic crude oil, now controlled at far below world prices, which in three annual steps would be raised to world levels.

Carter also proposed that the price of natural gas be allowed to rise, though he did not want to abandon federal price controls entirely.

Once gas price controls were eased and the crude oil tax was in place, a second tax on industrial use of oil or natural gas to push industry and utilities to use of abundant coal was expected to be the big oil saver in the program, accounting for almost half [WORD ILLEGIBLE] 4.5 million barrels a day in [WORD ILLEGIBLE] savings by the mid-1980s.

The president also wanted a standby tax on gasoline - which congress promptly rejected - and a tax on gas-guzzling cars, which, though likely to save little petroleum, would be a sign of energy consciousness. In addition, he proposed rewarding with tax credits people who insulated their homes, sought imposition of energy standards on home appliances and urged that electric utilities be required to save energy by such actions as offering cheaper rates for off-peak consumption.

The House rather quickly and under heavy pressure from its Democratic leaders approved most of Carter's program. The Senate, which had more time to think it over and to hear from interest groups, rejected most of it last fall. The House version might have saved half to two-thirds as much oil as Carter was after, the Senate, far less.

House-Senate conferees have been trying ever since to resolve their differences. They have compromised out most nontax parts of the package. But the crude oil tax, the centerpiece, is considered by most observers to be dead.