Undated (AP) _ Nevada filed five lawsuits, and officials of Texas and Washington promised their own challenges to the Reagan administration's targeting one of the three states as the possible site of the nation's first nuclear waste repository.

Mississippi officials expressed guarded relief Wednesday after the U.S. Energy Deparment announced that their state and Utah were no longer potential sites for underground storage of 77,000 tons of spent nuclear fuel.

However, Utah officials said they might join the lawsuits in an effort to keep from being reconsidered.

''Politics is kind of like a baseball game and Yogi Berra said, 'It ain't over 'til it's over,''' Utah Gov. Norm Bangerter said. ''Until a site is selected and they start putting waste into the ground, it's not over.''

Selection of the three sites means six-year geological investigations requiring shafts up to 4,000 feet deep will begin at Yucca Mountain in Nevada; the Hanford Nuclear reservation in Washington; and Deaf Smith County, Texas.

The Energy Department also said a second permanent storage depot is not needed now, ending uncertainty for New Hampshire, Maine, Minnesota, Wisconsin, Virginia, North Carolina and Georgia, which had been under consideration.

The first repository, which is to open in 1998, four years after a president makes the selection, is supposed to protect waste from disturbances for 10,000 years.

Nevada Attorney General Brian McKay immediately filed five suits in the 9th U.S. Circuit Court of Appeals, contending that the selection process is illegal and designed to place Yucca Mountain - within the Nevada Test Site in southern Nevada - in a position as the only site under consideration, and that the DOE failed to acquire necessary jurisdictional controls over the mountain.

Washington Gov. Booth Gardner and Attorney General Ken Eikenberry said the DOE was playing politics and being less than scientific by including Hanford.

The state will file suit in the 9th U.S. Circuit Court of Appeals within weeks, also challenging the selection process, they said.

''I think it was essentially a political decision,'' Gardner said.

He held up a map showing where most of the nation's high-level radioactive wastes are produced - mostly in the East - and said, ''Guess where it's going?'' He pointed to the three Western sites.

Gardner said he believes Hanford will never be chosen on its own merits, but that he feared the Texas or Nevada sites might be eliminated for other scientific or political reasons, leaving Hanford the choice by default.

''If Nevada were to drop out because of earthquake faults and Texas because they have so many congressmen in Congress, it's pretty hard for me to step before the people of the state of Washington and say we have the safest site,'' he said.

Texas Attorney General Jim Mattox, who filed an unsuccessful lawsuit against the federal government after an unofficial December 1984 announcement that the Texas site was a finalist, said the state plans to sue again.

''DOE's announcement is no surprise to us, so it should come as no surprise to the federal government that we will see them at the courthouse as soon as possible,'' said Mattox. ''This is proving to be the biggest railroad job ever perpetuated by the federal government upon this state, and I intend to fight it tooth and nail.''

Attorneys for the Nuclear Waste Task Force Inc., an organization comprised of Panhandle landowners, citizen and commodity groups, said they expected to file a lawsuit today to delay and eventually stop the site studies.

Texas Agriculture Commissioner Jim Hightower said Deaf Smith County and other portions of the Panhandle could be damaged by drilling the testing shaft through the Ogallala Aquifer, the region's major water source. He also noted the number of food and agricultural operations in the area.

''Didn't we learn anything fromm the accident at Chernobyl, where essential food supplies for part of a continent were contaminated?'' Hightower asked, referring to last month's Soviet nuclear power plant disaster.

''I feel they would ruin the whole Texas Wheat Belt should the water get contaminated,'' said Deaf Smith farmer Anthony Paschel. ''If there's an accident here like there was in Russia a few weeks ago, then there won't be water left for a jackrabbit.''

In Mississippi, officials expressed relief that the Richton and Cypress Creek salt domes were no longer being considered.

''If the president would send me a letter, along with letters from the secretary of energy and everybody else up in Washington, saying that both were absolutely out of the running, then I'd come closer to believing it,'' said Jimmy Palmer, an aide to Gov. Bill Allain.

In Utah, Bangerter said because legal action or geological flaws in one of the three preferred sites could force reconsideration of the Davis Canyon site, the state may join the three finalists in their lawsuits.

''We will not allow ourselves to be selected by default,'' he said. ''We will take the position we always took, that is, not giving up any turf.''