The stock of Washington Gas Light Co. has climbed by almost one-third in two days of heavy trading since the company announced a natural gas discovery by one of its subsidiaries.

The stock closed yesterday at 29, up 2 1/2 from Monday's close and up 7 from Friday's closing price. Trading was heavy at 44,200 shares, in contrast to normal volume of several hundred shares.

The activity followed an announcement by WGL that an exploratory well in which a subsidiary, Crab Run Gas Co., has an interest had encountered "a significant flow of natural gas."

According to WGL, gas was struck at a depth of 15,335 feet in a well in the deep Anadarko Basin area of Oklahoma. A spokesman for the company said that the well produces as much gas in 36 hours as any one of the company's other wells produces in a month, with a preliminary estimated flow rate of 75 million to 100 million cubic feet a day.

The company said that the discovery will have no impact on consumer rates.

Crab Run has a 19 percent working interest in the well. Crab Run is the only WGL subsidiary strictly involved in exploration.

In a separate announcement, Columbia Gas System said that a subsidiary has agreed to buy 50 percent of the gas produced by Chevron U.S.A. Inc. in the Whitney Canyon and Carter Creek areas of southwest Wyoming. That share is estimated at more than 500 billion cubic feet, which will come from a gas-processing plant to be built by Chevron.

The gas will be delivered over a 15-year period, with deliveries expected to begin in 1982.