Steuart Petroleum Co., a closely held family business, last week agreed to sell half of its stock to Agip Petroli, Italy's largest refiner and distributor of oil products.

Steuart Petroleum is the principal supplier of home heating oil to the metropolitan area, selling its products to Potomac Electric and Power Co. and the federal government, as well as to the District school system.

The 86-year-old company is the largest subsidiary of Steuart Investment Co., a diversified holding company owned by the Steuart family. The oil company's sales are estimated at more than $450 million.

The Italian company has signed a letter of intent to buy 50 percent of the company from the family for an undisclosed price. The deal is expected to be completed by August. Management will remain the same.

"Agip is to Italy what Exxon is to the United States," said Leonard P. Steuart II, chairman and chief executive officer of the District-based company.

"We're very pleased with the deal. Our partners are well experienced in the international oil business . . . . We'll benefit from that."

Agip, a subsidiary of Italy's $35 billion state energy group Ente Nazionale Idrocarburi (ENI), is the largest refiner and distributor of oil products in Italy. The company reports about $7 billion in revenue.

Enzo Vicusi, vice chairman of Agip, said the investment was a "logical step" for the company, which wanted to strengthen its foothold in the U.S. oil market. "This brings us closer to the customer," Vicusi said.

For 15 years, Agip has supplied major U.S companies with oil products through one of its 12 U.S. subsidiaries, Agip USA Inc. of New York.

Steuart said his company was approached by Agip just over nine months ago. Earlier in 1986, Steuart Petroleum had called off a deal to sell half of the company to Venezuela's state-owned oil concern, Pertoleos de Venezuela.

The District company plans to use the additional capital to expand by acquisition, Steuart said. A team of consultants has been formed to look at possible markets for expansion.

Steuart said he doubted that company would move west of the Mississippi River, but it may look to buy service station chains or retail fuel companies.

The company will continue to market industrial heating oil and home heat oil. The comany also is a wholesaler of gasoline products.

Steuart Petroleum generates about 75 percent of Steuart Investments revenue. The holding company also has ventures in a fish business in Washington state, a fleet of fishing vessels and a tug and barge business on the East Coast.

Biotech Research Laboratories Inc., a Rockville-based company best known for its AIDS antibody test, has moved into the veterinary market with the introduction of a test and treatment for foals that don't develop immune systems.

Foals are born without immunity systems and receive antibodies needed for survivial from mares during the first milking.

About 25 percent of newborn foals, for various reasons, don't receive the required immunoglobulin G (IGG), Biotech Research said. The test, Immuno-Stik, enables veternarians to determine the level of IGG in a foal's blood.

If the level is low, the company also has developed an Equine IGG product that can be given orally to the foal. The products could save the lives of the newborn horses, the company said.

The product is produced and purified from the serum of hyperimmunized horses. The company estimates that potential worldwide market for the IGG test is more than $60 million.

More than 100 of the 143 sales associates at Hugh T. Peck Properties Inc. of Bethesda have opted to join Long & Foster Realtors of Fairfax after the Peck family said it would dissolve its residential brokerage operations.

Hugh T. Peck will continue to operate Hugh T. Peck Property Management and Hugh T. Peck Insurance Service Inc. Its residential real estate operations had accounted for $75 million in sales for 1986, Long & Foster said.

Quadelta Inc., a small consulting firm in Falls Church, has received its first major contract from the U.S. Navy for support of the Space and Naval Warfare Systems Command.

The company, which has worked with the Navy for three years, received a $4.5 million, 4 1/2-year contract to provide engineering and management consulting to the command.

The company will provide consulting on procurement equipment and electronics and continue to provide coverage for the "Sparwar" test and evaluation status report. It also will teach a course to Navy personnel on the test and evaluation process.

Two small Rockville communications firms, B2 Communications Inc. and C&R Graphics, have merged their practices to combine their public relations and advertising expertise.

The combined company will operate as B2 Communications, occupying a new office on Executive Blvd. in Rockville. Prior to the arrangement, B2 had specialized in public relations and C&R Graphics had concentrated on graphic design and advertising.

Clients of the two firms have included Hyatt Regency Bethesda, McLean Hilton, Smithy Braedon Co. and China Investment & Trade Co.

The Weihe Partnership has formed a joint venture with Pierluigi Nervi & Associates of Rome to expand the services of both firms.

The Nervi Group, with offices in Florence, Zurich and Houston, will establish a Washington office in the Weihe Partnership office on K St. NW. Andrew Pica, vice president of development for Nervi, will head the Italian company's District operations.

Booz, Allen & Hamilton of Arlington recently was awarded three separate contracts from the U.S. Navy Industrial Improvement Program for work at naval aviation depots, shipyards and public work centers.

The contracts are worth $20 million. Booz, Allen, which has worked with the Navy on naval aviation and shipbuilding for more than 30 years, will attempt to reduce the Navy's ship and aircraft repair costs.

Data Measurement Corp., a Gaithersburg company that manufactures computerized systems to measure and control industrial products, last week signed an agreement to acquire part of an Oklahoma company for an undisclosed price.

The company plans to buy the instrument systems division of The Fife Corp., a subsidiary of Rexnord Inc. The division, which employs about 40 people, also works in the computerized systems manufacturing industry but concentrates in software development, a company spokesperson said.

The division operates facilities in Oklahoma and West Germany, as well as six field offices nationwide. The deal is expected to be completed by August, a Data Measurement spokesman said.

"Data Measurement's traditional customer base has been the metals business," said Dominique Gignoux, chairman and president of Data Measurement, "whereas Fife's cutomer base consists of a nonmetal business -- producers of fibreglass, flooring materials, paper, rubber, vinyl . . . . This acquisition will position the company to become a leading supplier throughout the market spectrum."

John Adams Associates Inc. of the District and Currey Communications of Charleston, W.Va., have affiliated to provide joint public relations and community relations services. Both firms specialize in environmental, health and public safety communciations.

A group of Indian-American business people, preparing to establish a new bank in the District to service their community, has received preliminary approval from the Comptroller of the Currency to charter the First Liberty National Bank.

The bank will be the first in the metropolitan area and the third nationwide to cater to the Indian community. It will be located on the ground floor of a building at 1146 19th St. NW.

The group expects to offer shares of the bank's holding company, First Liberty Bancorp, shortly and the bank is expected to be opened in the fall.

The lead organizer is economist Vidya N. Singh of Hyattsville. A native of the Indian state of Bihar and now a U.S. citizen, he has lived in this region for 20 years.

The Forte Group of Creative Companies, an Alexandria company that provides graphics arts and presentation services, recently bought a privately held Cleveland company for an undisclosed price.

The Forte Group, which oversees four companies in Virginia and one company in Baltimore, bought Projections Inc. of Cleveland and renamed it Carousel Cleveland. Carousel Cleveland will continue to service the former company's clients, which include companies in the manufacturing, oil and insurance fields.