Manor Care Inc. has signed a $10 million, 8-year credit agreement with the Riggs National Bank. Manor Care said it will use the funds for acquistion purposes.

Manor Care President J. Calvin Kaylor said the new line of credit is in addition to the $23 million in cash the firm received when it sold its common stock of the Hillhave Corp. on July 31. Last month, Kaylor told Manor Care shareholders that top priority has been given to the study of acquistions of nursing homes and hospitals.

JOINT VENTURE: The Rouse Co. of Columbia has entered into a joint venture with JMB Realty Corp. of Chicago for the ownership and management of Duchess Mall in Fishkill, N.Y. This is the fourth time the two firms have joined forces in shopping center ventures.

LOAN INSURANCE: The Federal Maritime Commission will recommend approval of loan insurance to underwrite construction of three tugbarge vessels at Bethlehem Steel Corp's Sparrows Point Shipyard, Rep. Clarence D. Long (D-Md.) said.

Long said Wednesday maritime officials told him they would suggest approval of loan insurance for the $180.9 million project for the Amerada Hess Corp.

REVOCATION: The Securities and Exchange Commission has revoked the registration of Group Financial Services Inc., a Rockville investment adviser. Earlier this year, the SEC division of enforcement accused the firm of violating federal securities law in connection with the sale of an insurance-mutal fund package known as Univest or economic survival package.

FIRM PICKS LEESBURG: The Rehau Plastiks Group, a Swiss plastics manufacturing firm, will establish a technical center and headquaters in Leesburg. The center will be housed in the old Westinghouse building on Edwards Ferry Road. The facility eventually will employ 150 persons.

FIRM BOUGHT: Media Solutions Corp., a Falls Church media consulting firm, has acquired Litte River Promotions of Annadale of an undisclosed amount. Little River is involved in shopping center promotion and marketing. a