Wyoming’s Simpson Expected to Retire From Senate : Politics: GOP stalwart will leave after three terms. Report comes on the day Oregon Republican Mark O. Hatfield confirms he will not seek reelection.

Republican Sen. Alan K. Simpson, who remained hugely popular among Wyoming voters even as he occasionally raised hackles in Washington with his acerbic wit and attacks on the media, will retire when his third term ends in 1996, Republican sources said Friday.

The report on Simpson came the same day that Sen. Mark O. Hatfield (R-Ore.), as expected, formally declared that he would not seek reelection next year. The 73-year-old Hatfield, first elected in 1966, returned to Oregon to announce his retirement, saying, “Thirty years of voluntary separation from my state has been enough.”

Similarly, Simpson is expected to use an appearance before a hometown crowd in Cody today to announce that he will not seek a fourth term, according to the sources. Simpson’s office would not comment on the nature of his speech except to say it would be a major announcement regarding his political future.

Simpson, 64, would be the 12th senator to announce plans to retire in 1996. The last time that many senators gave up their seats was a century ago, in 1896.

In the Senate, Simpson was a driving force behind an overhaul of the nation’s immigration laws in the 1980s, co-authoring legislation that became named for him and his then-House colleague, Democrat Romano L. Mazzoli of Kentucky.

Elected Senate Republican whip in 1984, Simpson also was noted for his battles against environmental regulations. For instance, he sought to exempt rock and coal mine dust from air quality measurements and fought the Endangered Species Act.

But his support for abortion rights and his moderate positions on other cultural issues cost him support among conservatives and was the key factor in his loss of the whip post when Republicans took control of the Senate last year for the first time since 1986.

Most recently, Simpson has taken on entitlement programs and their most adamant defenders. He has urged Congress to slow the growth of such programs and sought to limit the clout of the American Assn. of Retired Persons, which he said should be forced to pay income taxes.

A frequent critic of the media, he drew widespread attention when he characterized CNN correspondent Peter Arnett as an Iraqi sympathizer during the Persian Gulf War. He later tempered his remarks.

He also gained the spotlight with his fierce criticism of Anita Faye Hill during the Senate confirmation hearings of Supreme Court Justice Clarence Thomas, whom Hill had accused of sexual harassment.

Simpson, whose family has been a political institution in Wyoming, won his first U.S. Senate race in 1978 and handily won reelection in 1984 and 1990.