SOUTHWESTERN ENERGY <SWN>, ARKLA <ALG> SET PACT Southwestern Energy Co said it reached an agreement with Arkla Energy Resources for Arkla to carry gas owned by Southwestern subsidiaries. Under the agreement, the interstate pipeline division of Arkla Inc will carry up to 25 mln cubic feet of gas a day until Dec 31, 1987, and, subject to capacity, up to 50 mln cubic feet a day in 1988 and 75 mln feet a day for the rest of the pact. Payment terms vary depending on the type of service provided, a Southwestern spokesman said. The deal is effective March one, 1987, expires July one, 1997, and is renewable yearly thereafter, he said. The pact calls for transmission of gas owned by Arkansas Western Gas Co, Seeco Inc, Arkansas Gas Gathering Co and Southwestern Energy Production Co, Southwestern Energy said.