Steuart Petroleum Co., the Washington fuel distributor whose plans to build an oil refinery in St. Mary's County, Md., were blocked by local opposition, has formed a partnership with two other firms to open a refinery in North Carolina.

Steuart, the largest heating oil firm in the Washington area, will own a one-third share of a proposed 150,000-barrel-a-day refinery proposed for Brunswick County, N.C.

The proposed refinery would cost an estimated $350 million to $450 million to build and would require 2,000 workers to build and 250 to operate.

In two other expansion moves, president Leonard Steuart said the family-owned firm has purchased Colonial Fuel Company, a home heating oil retailer, and opened a 300,000-barrel fuel terminal at Cockpit Point on the Potomac River in Prince William County, Va.

The purchase of Colonial, which provides oil to 5,500 customers, is the first move into retail marketing of home heating fuels for the Steuart firm.

Primarily a distributor or wholesaler, Steuart is the local Chevron gasoline distributor, sells 200 million gallons of home heating oil a year and is the largest local distributor of residual heating oil used by power plants, factories, large buildings and the government.

Steuart's partners in the proposed refinery are Crown Central Petroleum Corp. of Baltimore, which will own 62 1/2 percent. and Federal Paper Board Corp. of Montvale, N.J., which will own 5 percent.

The Steuart president said the North Carolina refinery is the company's alternative to the plant it tried to build at Piney Point, Md., on the Potomac River.

The Piney Point project was canceled in 1974 after local residents voted 2 to 1 against it in a referendum, the Maryland legislature passed two bills to block its construction and Gov. Marvin Mandel said the state would not issue permits to operate the plant.

"The attitude of the people in North Carolina has been very different," said Steuart. The governor of the state hailed the announcement of the proposed refinery as "a great day for the state of North Carolina."

Steuart said building the oil processing plant in North Carolina will cost substantially more than it would have to put the refinery in Maryland.

"We already have 75 percent of a refinery there," where there are an unloading pier, storage tanks and distribution center, he explained.

Because of opposition, no major refineries have been built on the East Coast in nearly 20 years and the North Carolina project faces at least two years of environmental and other reviews.

The 1,900-acre site has already been designated as "suitable for a refinery" by the state.

"The closest approximation of a start-up date possible at this stage is sometime in the early 1980s" Steuart said.

Steuart said the plant will refine imported oil, but no source of raw material has been selected yet because, "there's plenty of crude around." The refinery will be designed to produce mostly gasoline and home heating oils.