Sen. John G. Tower (R-Tex.), who took over Lyndon B. Johnson's Senate seat in 1961 and rose to the chairmanship of the Armed Services Committee, announced yesterday that he will not seek reelection in 1984.

Tower's decision set off a scramble in the Republican Party to find a replacement, while Democrats immediately moved Texas onto the list of seats they hope to win next year in their bid to recapture control of the Senate.

"I have recently made a personal decision that after 24 years of elective service and at the peak of my productivity, I should step aside and pursue other avenues of endeavor," Tower, 57, said at a news conference in the state capitol in Austin.

The diminutive former college professor criticized the Senate as a "multi-layered bureaucracy." And Texas Republicans said Tower is telling supporters he is simply "fed up" with the institution. He was visibly angered at times over the recent filibuster of funds for the MX missile.

Polls, including his own, indicated that Tower was favored to win reelection but faced a tough race, as he did in 1978. They also showed considerable defection by Hispanics, whom Tower had successfully courted in the past and who helped reelect him last time.

Tower already has raised an estimated $1.5 million in campaign funds. It is widely expected that he will use this money to aid other Republican candidates.

At yesterday's news conference he said he will work for President Reagan in Texas if the president, as expected, seeks reelection.

Tower is the second prominent Republican senator this year to announce his retirement. The first was Senate Majority Leader Howard H. Baker (R-Tenn.).

Republican sources said yesterday that Sen. Charles H. Percy (R-Ill.), who faces a primary challenge and a difficult reelection battle, might join the list of retirees. But Percy's office strongly denied the speculation.

Tower's retirement deprives Reagan of an unyielding champion of a strong military. But the next Armed Services chairman probably will be similarly inclined regardless of whether the Republicans retain control of the Senate.

The next senior Republicans on the committee are Strom Thurmond (R-S.C.) and Barry Goldwater (R-Ariz.) and the senior Democrats are Henry M. Jackson (D-Wash.) and former chairman John C. Stennis (D-Miss.).

Tower said that he will return to Texas after his retirement and deflected questions about his interest in becoming secretary of Defense in a second Reagan administration.

"I have been offered no such appointment, nor do I expect one," Tower said.

Tower unsuccessfully bid for the job when Reagan took office in 1981.

There appears to be no shortage of candidates interested in succeeding Tower.

Rep. Ron Paul (R-Tex.) of Houston and "Boll Weevil" Rep. Kent R. Hance (D-Tex.) got the jump on others by announcing their candidacy yesterday.

Also expected to join the race for the Republican nomination for the seat Tower now holds is Rep. Phil Gramm (R-Tex.). A former Democratic "Boll Weevil," the congressman was reelected to his seat as a Republican after he resigned to protest the Democrats' knocking him off the Budget Committee.

White House chief of staff James A. Baker III, who lost a race for Texas attorney general in 1978, dismissed as "baloney" reports that he might be interested in the Senate seat. Reagan administration sources said Baker would welcome leaving his highly visible and controversial White House post, and other Republicans indicated that Baker might not rule it out at this time.

In a statement read to reporters by presidential spokesman Larry Speakes as Reagan returned to Los Angeles from Seattle yesterday, James Baker said, "I hope Sen. Tower will reconsider his decision not to seek reelection. I'm not a candidate for that post."

But officials close to Baker said he is leaving himself a little "running room" to examine the Texas political situation before making a final decision.

Meanwhile, an associate of former governor Bill Clements (R), who lost his reelection bid last November, said he strongly doubts that Clements will enter the race.

Other possible Republican candidates include Rep. Bill Archer of Houston; Bob Mossbacher, who was finance chairman for Vice President Bush's presidential campaign in 1980; Anne Armstrong, former ambassador to Great Britain; H. Ross Perot, a wealthy Dallas businessman who now heads a Texas task force on education, and state Sen. Walter Mengden.

Although Tower's polls showed him running ahead of potential challengers, he faced a difficult reelection contest. In 1978, Tower defeated former representative Robert Kreuger (D) by just 12,000 votes.

Texas polls showed Tower running ahead of potential rivals but vulnerable.

In addition, Tower would have had to fight to maintain his support in the Hispanic community, which turned sharply against the Republican Party in Texas last fall. Also, the state's Republican Party is badly divided in the wake of Clements' defeat last November.

The retirement also set off a Democratic scramble. Two announced candidates, Kreuger and state Sen. Lloyd Doggett, said Tower's departure boosted their chances. But they are now likely to find themselves in a crowded primary.

Former governor Dolph Briscoe was on the brink of entering the race. Tower's retirement brought reports that other Democrats might now join in.