The Securities and Exchange Commission is investigating whether inside information was used to make profits on Texas Instruments stock and stock options before the shares plunged $50 apiece last week.

The Chicago Board of Options Exchange reported volume in Texas Instruments stock options doubled last week just before the company revealed it expected to lose $100 million in the second quarter.

The price of an option to sell 100 shares of Texas Instruments at $150 a share jumped from $250 to $4,200 after the company announcement. The value of the options soared because the contracts allowed speculators to sell the stock for $150 a share when the market price was $50 less than that. After dropping to the $100 range, the stock rebounded to $118 yesterday.

The SEC does not comment on pending investigations. Charles Dodson, branch manager of Prudential Bache in Lubbock, Tex., confirmed that the SEC asked him for information on customers trading TI options. He added it was his "impression" there was no violation of the law because the activity he witnessed was in line with usual trading patterns. Texas Instruments home computers are made in Lubbock.

The agency is also said to be concerned about a 295,000-share block of Texas Instruments stock that was sold through Salomon Brothers in New York on the day prior to the announcement. The stock was sold below market value. The seller has not been identified.

Texas Instruments attributed its expected loss to lower than anticipated sales of its home computer. Sales have been slumping because of a price war.

Other computer company stocks also declined after the Texas Instruments announcement.