A detailed contingency plan for establishing a national gasoline rationing system was sent to Congress by the Ford administration the day before President Carter took office.

Drafted by the Federal Energy Administration, it is part of a package of emergency contingency plans that could be implemented in the face of a new Arab oil boycott. The plans are required by the 1975 Energy Act.

As planned by the FEA, the complex national system is designed to cut annual gasoline consumption an estimated 21 per cent through the use of coupons and gasoline ration credits.

To supervise the system, FEA foresees the need for an 87,000-person work force, 40,000 coupon distribution sites and an annual cost of $1.9 billion.

The system would be financed by 2.3-cents-per-gallon increase in the cost of gasoline.

Under the 1975 energy law, the contingent gasoline rationing system could not be implemented by a President without specific congressional approval.

The plan establishes five categories of gasoline users - three for government and private concerns and two for individuals.

Each individual with a driver's license would be allocated eight five-gallon ration coupons for each ration period. The ration period is expected to be a month but could be five or six weeks depending upon the severity of the shortage.

Individuals with hardships - such as being handicapped or in need of gasoline for commuting - would apply for added hardship coupons to be distributed by specially established local ration boards.

Government, industry and commercial vehicle users would get ration credits, not coupons, which FEA would desposit each month at a designated commercial bank, savings and loan institution or credit union. The commercial user would draw from his credit balance through the use of a checking system.

Commercial allotments would be based on normal usage. Government, mass-transit operations and food producers would receive all the gasoline they require.

Sanitary systems, energy distributors, and others in a second category of special service woule get average past usage. Nonessential firms would ge supplies equivalent to 90 per cent of past consumption.

Gasoline could be sold only in five-gallon lots and only purchasers who had coupons or ration credits.

Under the plan, the selling or free trading of coupons and credits by those who did not need the amount allocated to them would be permitted. It was estimated that the value of a five-gallon coupon could rise as high as $5.25, based on current usage.

The FEA said it would audit refiners and importers, and that the rest of the system would be "self-enforcing."

The contingency plan has some reserve gasoline supplies built into it. A harship reserve totaling 3 per cent of supplies would be available and the FEA would maintain a "national ration reserve" that would equal 1 per cent of supplies.

Since drivers' licenses would be the key to getting the coupons, the FEA forecast a rush on motor vehicle bureaus involving almost 15 million currently unlicense drivers.

The first foul-up in the proposed rationing system already has taken place.

The contingency plan was supposed to be delivered to Congress by last June. It was dispatched to House Speaker Thomas P. (Tip) O'Keill Jr. (D-Mass.) on Jan. 19, the day before Carter's inauguration.

The Senate copy, supposedly sent out the same day, has not been found. "It apparently got to (Vic President) Rockefeller while he was moving out," an aide to Sen. Henry M. Jackson (D-Wash.), chairman of the Senate Interior Committee, said yesterday.