Security Pacific Corp. said it has received approval from the Federal Reserve Board to acquire majority ownership in Hoare Govett Ltd., a leading stock brokerage firm in Great Britain . . . Tenneco Oil Exploration & Production, a unit of Tenneco, let go about 400 employees because of continued falling oil prices, company officials said . . . Appliance maker Maytag Co. said it spent a record $30.3 million for capital improvements in 1985 and and that it expects to spend $5 million more than that this year . . . The Investment Company Institute reported that the assets of the nation's 362 money market mutual funds rose $1.44 billion in the week ended March 12 . . . MCI Communications reported that it has reached an agreement with Italcable, the Italian communications agency, to provide international telephone service to Italy, pending approval by the FCC.