he South Texas Nuclear Project began 10 years ago as a $1 billion solution to the growing energy needs of four Texas cities. Today it is a $4.5 billion mess, still years from completion and looking increasingly unattractive to its original investors.

In the past two weeks, the project has undergone a mid-life crisis:

The managing partner, Houston Light & Power Co., on Sept. 24 fired the Houston-based firm of Brown and Root Inc. as the architectural engineers on the project and replaced it with Bechtel Power Corp. of San Francisco. Brown and Root will remain in charge of construction on the project.

The Austin City Council on Sept. 17 voted 5 to 2 to put a referendum to the voters on Nov. 3 on whether to sell the city's share of the project.

And the board of directors of City Public Service in San Antonio on Sept. 28 ordered its staff to prepare a set of energy alternatives for the city that could be a prelude for San Antonio backing out of the project. The report is due Oct. 26.

The project's problems are the latest indication that nuclear power is plagued not only by questions of safety but increasingly with concerns over costs.

The firing of Brown and Root coincided with the company's release of the latest cost and completion estimates for the 2,500-megawatt project, which has been under construction since 1973 in Bay City, Tex. Brown and Root projected the cost of the project at $4.4 billion to The south Texas project's problems are the latest indication that nuclear power is plagued not only by questions of safety but also increasingly with concerns over costs. $4.8 billion and said the first of two reactor units would begin fuel loading in late 1986. Already $1.6 billion has been spent on the plant.

The company's original projection, issued in 1973, called for completion of the first unit in 1980 and the second in 1982 at a combined cost of $1 billion. The cost was raised to $2.7 billion in 1979, with completion pushed back to 1984 for the first unit and 1986 for the second.

The south Texas project has been plagued by problems. In the spring of 1980, the Nuclear Regulatory Commission fined Houston Light & Power $100,000 and issued a show-cause order requiring the company to demonstrate why it should be allowed to continue the project. The fines resulted from inadequacies in the project's quality assurance and quality control programs and from intimidation of inspectors by workers. Houston Light & Power voluntarily stopped work on the project in March, 1980, after irregularities were discovered in some of the welding and concrete work.

Those problems were cited in an NRC study recently made public by Ralph Nader's Critical Mass Energy Project. The South Texas Nuclear Project was one of 12 projects rated below average among 78 under construction.

The problems also prompted the NRC to order hearings on the quality assurance program in advance of full-scale licensing hearings. Those hearings are in progress.

Officials at Houston Light & Power said the new cost-completion projections--which it has disavowed--had nothing to do with the decision to replace Brown and Root, which had no prior experience building a nuclear power plant. Bechtel has worked on more than three dozen.

Don Beeth, director of nuclear information for Houston Light & Power, said Brown and Root was fired because of its inability to do the engineering work fast enough. "The issue was not the quality of engineering but the quantity of engineering," he said.

He also defended the quality of the construction work on the project to date, a target of the project's critics. "Brown and Root's construction Austin voters have had several referendums on nuclear power, the most recent coming shortly after the March, 1979, accident at the Three Mile Island plant near Harrisburg, Pa. quality we have always felt to be good," Beeth said. "The most difficult problem is getting drawings to the field in sufficient numbers to support construction activities."

Richard Udell of Critical Mass said the south Texas project "ranks among the three or four worst" under construction. "We are talking here about a potential time bomb," he said. "Not only is public health and safety held hostage, it's a financial problem for consumers."

Consumer restlessness has prompted the recent actions in Austin and San Antonio, but Beeth said the decision to fire Brown and Root had nothing to do with increasing public dissatisfaction. "The public relations aspect of this was nonexistent," he said.

The project is jointly owned by four partners: Houston Light & Power Co., with a 30.8 percent share; the city of San Antonio, with a 28 percent share; Central Power & Light Co. of Corpus Christi, with a 25.2 percent share, and the city of Austin, with a 16 percent share.

Austin voters have had several referendums on nuclear power, the most recent coming shortly after the March, 1979, accident at the Three Mile Island plant near Harrisburg, Pa. In that one, voters narrowly decided to continue the project.

San Antonio's City Public Service board decided to reevaluate its role in the project because it may need more energy before the nuclear plant is completed.

"What prompted the review is not only the great increase in the cost, but also the slippage of the schedule," said Bob McCullough, public relations assistant for the utility company. "We need more energy by 1988. Brown and Root says unit No. 1 would give us power by early 1987. That doesn't give us much leeway."

Bechtel plans to issue its own projections on cost and completion in six to nine months.

Beeth said his company is not worried about the coming Austin referendum. "I don't believe Austin has the power to take an action that will either assure the project's success or cripple it," he said.