Two small aviation companies signed an agreement last week bringing them under the wing of Piedmont Aviation Inc.

But passengers will hardly notice a difference: Both Henson Aviation Inc. of Salisbury, Md., and Jetstream International Inc. of Erie, Pa., have operated under Piedmont's winged logo for quite some time.

Henson, Piedmont's exclusive regional airline, is 60 percent owned by the larger company and will become a fully owned subsidiary by 1988. Jetstream has operated as a Piedmont commuter airline under a marketing agreement since November 1985.

Piedmont's purchase of Jetstream will be indirect: Henson will acquire Jetstream by Aug. 1, subject to approval from Jetstream shareholders. Members of Jetstream's board of directors, who hold 51 percent of the company' shares, already have signed the agreement. The value of the transaction was not disclosed.

"This is one of the simplest and cleanest ways of acquiring one of our commuter airlines," a Piedmont spokesman said. "Jetstream has not had a profitable year since its inception in 1983 , and we feel if we place the company to service our Dayton, Ohio hub we can turn a profit in 60 days."

Under the agreement, Jetstream will become the primary commuter partner for Piedmont's major midwestern hub in Dayton. Henson will continue to operate its fleet of 29 aircraft as the regional airline for the company.

"We feed the Piedmont hubs, that's our purpose in life," said Richard A. Henson, who founded Henson Aviation as a one-pilot operation in 1931. "We pick up the passengers and carry them to the hubs, where they are transferred to Piedmont's trunk carriers."

This acquisition also divides the Piedmont commuter and regional airlines into two separate corporations. Henson had operated both commuter and regional lines but will phase out the commuter operations after the acquisition. Federal aviation regulations impose different restrictions on commuter airlines, whose aircraft have 19 or fewer seats, and regional airlines, which operate aircraft with more than 30 seats. The regulations make it more costly to operate both airlines under one company.

"Ultimately, we will be able to better service communities by interchanging the 19-seat carriers with the over 30-seat carriers depending on the density of the routes," Henson said. "The acquisition streamlines operations, and it makes economic sense to separate the two levels of carriers into two corporations."

Cal Humphrey, president of Jetstream, said his company is excited about the plan. "I think it's excellent for the employes, who have put in such hard work since the company was started. It's only going to get better. With Piedmont behind us, the acquisition opens up opportunities to expand."

Last year, Piedmont reported $1 billion in revenue and $62 million in profits.

Continental Federal Savings Bank of Fairfax finalized agreements last week to secure a share of the boat financing business.

Continental Federal signed an agreement with the Boat Owners Association of the United States to provide marine financing to the association's 200,000 members. The bank will provide financing and refinacing for existing marine loans.

"This agreement provides us with several million dollars of marine loans each year, and the bank has segregated its financing to the large-craft market, which means loans in excess of $25,000," said Ernest L. Tressler, executive vice president and chief loan officer of the bank. The bank moved into the marine financing industry last December when it purchased a local marine financing company, Maryland Marine.

Systematics General Corp. of Sterling, Va., began delivering a new line of high-security computers to the government last week, under a contract that is estimated at $700,000.

The government contracted Systematics General to retool Wyse Technology Corp.'s IBM-compatible personal computers to meet its TEMPEST requirements. TEMPEST makes equipment tamper-proof.

Systematics General is a subsidiary of Atlantic Research Corp.

Adolph Coors Co. has awarded the contract to build waste- and water-treatment facilities at its Shenandoah Brewery near Elkton, Va., to The Polote Corp., a minority-owned construction firm based in Savannah, Ga.

The brewing facilities, Coors' first on the East Coast, will be in operation by April 1987, the company said.

Under the $3.7 million contract, Polote will build a fire-pump house, water- and waste-treatment plants and two well-pump houses on the site. Polote plans to hire employes from Virginia.

The contract is the largest single one ever awarded to a minority firm by Coors, the company said.

Westinghouse Electric Corp. formed a joint venture with a British aerospace company last week to produce airships for the U.S. Navy. Westinghouse and Airship Industries Ltd. teamed up last year to work on a U.S. Navy airship study, to be completed this year. The joint venture, Airship USA, plans to "bid and win the contract for the U.S. Navy Proof of Concept Airship," and is "a natural follow-on" to the earlier contract for the study.

Airship USA will be located in Weeksville, N.C., where a Westinghouse subsidiary and Airship Industries currently share facilities.

BASF Structural Materials Inc. will build a $20 million manufacturing plant near Williamsburg to be completed next summer, the company said last week. BASF Structural Materials is a subsidiary of the international chemical company BASF Corp.

The carbon fiber precursor plant will be located on the company's Williamsburg site, along with the divisional headquarters and two other plants. The company employs approximately 900 people at the facilities and expects to add 40 more upon plant completion.