ECONOMY T-bill yields rose at the government's weekly auction. The Treasury sold 13-week bills at an average discount of 7.55 percent, up from 7.41 percent last week, and 26-week bills at an average discount of 7.45 percent, up from 7.31 percent. The investment rate was 7.80 percent on the 13-week bills and 7.85 percent on the 26-week bills. The number of oil or gas rigs exploring in the United States fell by five this week to 987, according to Baker Highes Inc., an oil toolmaker. A company spokesman said the Persian Gulf situation has not yet pushed up the number, but he predicted the count would increase within two to four weeks if oil prices continue to rise. The Department of Veteran Affairs will issue about $293 million in mortgage certificates. First Boston Corp. will be lead manager. Construction contracts will decline by 7 percent this year as the nation struggles to pull out of a continuing building slump, according to a forecast by McGraw-Hill Information Services.

COMPANIES US Sprint will reorganize its long-distance sales and service division in the Reston area, resulting in a net loss of about 100 jobs. A spokeswoman said the move would result in some layoffs of local administrative staff and the hiring of some employees in the areas of sales and government systems. General Motors said it will give the United Auto Workers a contract offer this week designed to make the union pick GM as the target company for nationwide negotiations. Contracts covering more than 450,000 workers at GM, Ford and Chrysler expire Sept. 14, and the union is expected to choose its target company next week. Second National FSB of Salisbury, Md., said shareholders approved the formation of a holding company, Second National Bancorporation. The bank said the action will allow Second National greater flexibility in raising capital and assist in product development and mergers and acquisitions. Eli Lilly and Co. said it will spend $540 million on an expansion that will add 1,000 people to the company's work force in Indianapolis. END NOTESSystems Center of Reston paid Informed Management Environment of Houston about $2.4 million for the rights to software that manages the IBM computer known as AS/400. The AS/400 line has been IBM's most successful entry in the mid-price range for computer systems used by companies, Systems Center said. Interco will ask bondholders to exchange their bonds for 95 percent of the company's common stock and other considerations under a restructuring plan. The footwear and furniture maker has been struggling to pay off its large junk bond debt since it borrowed $1.65 billion in 1988 to fend off a hostile takeover by Steven and Michael Rales of Washington. United Artists Entertainment signed a $2.8 billion agreement that refinances the company's debt. The transaction also will improve the company's ability to replace short-term floating funds with long-term fixed rate funds and will provide funding availability to pursue future opportunities, the company said. Volkswagen, following the lead of other major automakers, said it will open a design studio in Southern California.

INTERNATIONAL British Petroleum said it will auction off its gas exploration and production holding company in the Netherlands.

EARNINGS K mart reported that earnings rose 2 percent in second quarter and 4 percent in the first half.

PEOPLE Charles Keating, chairman of the former parent of defunct Lincoln Savings and Loan, is close to a settlement of the government's suit to force disclosure of his finances, a judge said. After both sides made initial arguments at a hearing, the judge said there was a ''strong possibility'' of a resolution by today. Donald Trump reached an agreement with a group representing about 60 contractors who say the developer owed them $60 million for work on the Taj Mahal casino-hotel, the creditors said. The announcement was made one day before the New Jersey Casino Control Commission is scheduled to rule on whether Trump can use the Taj Mahal in Atlantic City and his two other casinos as collateral for a $65 million emergency loan.

ODD LOTS Chase Manhattan plans to install Russian language teller machines in branches in Brooklyn and Manhattan to serve the thousands of Jews arriving in New York from the Soviet Union. The American Stock Exchange reported a membership seat sold at its lowest level in more than 10 years, $107,500, down $10,000 from the last sale Aug. 3. A seat on the New York Stock Exchange sold for $310,000, down $10,000 from the last sale Aug. 15. Hyatt is replacing the 19-year-old four-leaf clover logo for its hotels and resorts with a rectangular one using stylized lettering that is designed to project a more contemporary image.