HOUSTON -A leak discovered under a reactor at a Texas nuclear plant is nothing on the scale of a similar problem at an Ohio reactor, the Nuclear Regulatory Commission said Monday.

``There's a huge difference in perspective here,'' said Victor Dricks, spokesman for the commission.

The leak at the South Texas Project plant southwest of Houston left a small amount of boric acid residue from cooling water. The accumulation, discovered April 12, was smaller than an aspirin tablet.

Last summer, at the Davis-Besse nuclear plant east of Toledo, Dricks said a leak involved a ``massive amount of boric acid crystal'' that required the use of shovels and crowbars to remove the residue.

``It was that bad, and because it sat on top of the reactor vessel it had eaten a football-sized hole in the top of the reactor head,'' Dricks said.

The leak at the Texas plant is different because it occurred on the outside of two instrument guide tubes where they enter the bottom of one of two reactors.

Tests indicate the residue came from reactor coolant fluid, plant officials said, which would be unique among the 69 U.S. nuclear plants -- including South Texas and Davis-Besse -- that used pressurized water reactors.

``We just haven't seen this before,'' Dricks said, adding that stress corrosion cracking -- if that was the cause -- typically occurs at higher temperatures.

Dricks said inspectors found the problem at South Texas while following an inspection order related to the Davis-Besse problem.

Plant manager Ed Halpin said the leak was not fast-growing, and the guide tubes in question are not integral to the reactor's operation.

The South Texas plant must confer with the NRC before beginning any repair plan, and the plant has pledged not to restart until everything appears fixed.

The plant's other unit continues to operate at full power. The plant supplies power to customers from Houston to Austin and San Antonio to Corpus Christi.

FirstEnergy, owner of Ohio's Davis-Besse plant, said it is getting closer to restarting the plant in Oak Harbor. The plant has been shut down since February 2002. Substantial boric acid corrosion found in March 2002 on top of the reactor has kept the plant closed for repairs that probably will cost FirstEnergy more than $400 million.

Davis-Besse will do a pressure test of the reactor coolant system, which includes the reactor, in mid- to late May. It should be ready for restart about a month after the test is completed, company officials said.

FirstEnergy estimates the restart will come no sooner than mid-June. The NRC has its own inspections that can start only after repair work is completed at the plant.