ECONOMY T-bill yields were mixed. The Treasury auctioned 13-week bills at an average discount of 6.78 percent, down from 6.86 percent last week, and 26-week bills at an average of 6.77 percent, up from 6.74 percent. The investment rate was 6.99 percent on the 13-week bills and 7.11 percent on the 26-week bills.

COMPANIES Berkshire Hathaway, which is controlled by Omaha investor Warren Buffett, won permission from PS Group, an aircraft leasing and fuel distribution company, to own up to 45 percent of its common stock. Alaska Airlines announced plans for the first regularly scheduled passenger jet service from the West Coast to the Soviet Union. The service will begin June 17 between Anchorage and Magadan and Khabarovsk. First Liberty Bank of the District will get $4 million in new capital under an agreement with a private investor group headed by Washington attorney Stanton D. Anderson. Upon completion of the transaction, the investors will own about 50 percent of the common stock of First Liberty Bancorp, the bank's parent firm. Canadian Pacific and Conrail reached agreement on a disputed stretch of track between Buffalo and Niagara Falls, N.Y., clearing the way for CP to buy the ailing Delaware & Hudson Railway for $25 million. MCA, in a battle for theme park supremacy in Southern California, announced a $100 million expansion of Universal Studios Hollywood designed to bring tour visitors closer to the filmmaking process. Drexel Burnham Lambert accused federal thrift regulators of inventing and exaggerating some of its $6.8 billion in damages claims against the collapsed Wall Street firm. Drexel also accused the FDIC of seeking to blame it for the savings and loan industry collapse. Westwood Equities Corp., the parent of Ticor Title Insurance Co., has filed for protection from creditors under Chapter 11 of the U.S. Bankruptcy Code. The company, which listed $151.4 million in debts and $144 million in assets, said it would ask a Los Angeles bankruptcy judge to allow the $70 million sale of Ticor to Chicago Title & Trust Co. to go through as planned.

INTERNATIONAL Iran agreed to pay Arco $9 million, the last of hundreds of millions of dollars in so-called consortium claims of Western oil companies against Tehran. The settlement was for expropriation of Arco's operations in Iran during the 1979 Islamic revolution. NBC News and Nippon Television Network agreed on a joint news gathering venture, the third agreement this year between a U.S. network news division and a Japanese broadcaster. Daihatsu of Japan agreed to set up a joint venture with Piaggio of Italy to produce pickup trucks and vans in Pisa, Italy.

REGULATION The Business Roundtable, citing a study by a leading proxy- solicitation firm, urged the SEC to drop plans to change the rules governing proxy contests. The roundtable argued that the proposed changes would benefit large shareholders to the detriment of individual shareholders.

CONTRACTS FMC and General Dynamics received a $286 million Army contract to jointly design, build and test a prototype common chassis for four different armored vehicles for potential use at the turn of the century. Northrop received a $95 million Air Force contract for B-2 bomber items.

EARNINGS Nike said its second quarter earnings were up 58 percent.