The Senate Appropriations Committee yesterday approved a $20.8 billion energy and water spending bill for 1991 that provides tens of millions of dollars in nuclear, river navigation and research projects for southern and western committee members, including several facing reelection this fall.

Projects in the bill for the home state of Sen. J. Bennett Johnston (D-La.), chairman of the energy and water subcommittee, demonstrated the power available to Appropriations Committee incumbents. Johnston needs to win 50 percent of the vote in Louisiana's Oct. 6 open primary to preserve his seat without a general election.

Included in the measure was $92.6 million -- which the administration had not requested -- to enable the Corps of Engineers to continue the Red River waterway as far as Johnston's home town of Shreveport. The Bush budget had called for ending the project at Lock No. 3 at Colfax, La., but the new funding will finance construction of two additional locks.

The report also doubled the House appropriation for Corps of Engineers work on the Mississippi River ship channel between Baton Rouge and New Orleans; almost doubled the administration request for erosion projects in Louisiana's coastal wetlands; earmarked $12.5 million for the Biomedical Research Institute at the Louisiana State University Medical Center in Shreveport, and approved $750,000 for a Manufacturing Systems Engineering Research Center in Ruston, La.

In approving the full $318 million administration request for the atom-smashing Superconducting Super Collider (SSC) in Texas, the energy and water bill also moved along a project that may directly benefit Louisiana. General Dynamics and Grumman Corps. have both expressed interest in building plants in the state to construct the powerful magnets to be used in the particle accelerator outside Dallas.

Also faring well was Sen. Mark Hatfield (R-Ore.), whose power as ranking member of the Appropriations Committee and of Johnston's subcommittee is expected to add luster to his bid this fall for a fifth Senate term. The full committee recommended $12.5 million for the Neurosensory Research Center at the Oregon Health Sciences University. Hatfield also left his stamp on other parts of the bill dealing with nuclear and environmental issues of high interest to Oregon voters.

Meanwhile, retiring Sen. Jim McClure (R-Idaho) cashed in some of his prestige to come up with a final surge of funds for his home state, with special emphasis on the Idaho National Engineering Laboratory (INEL). Working in tandem, Hatfield and McClure cut back funds sought by the administration for developing nuclear reactors in space and directed the savings toward research into advanced commercial reactor technologies being developed by the Argonne National Laboratory, INEL and the General Electric Corp.

With McClure's support, the committee also approved an extra $12 million, sought recently by the administration but not included in the House-passed bill, for designing two new tritium production facilities to replace those shut down at Savannah River in South Carolina. The facilities will refurbish nuclear warheads containing tritium, and are being considered for the Savannah River facility and INEL.

Overall, the committee approved $3.2 billion for all nuclear waste cleanup activities, $402 million above the administration request but $84 million less than the House.

The bill is set to reach the Senate floor early next week.

Across the Capitol, the House Appropriations Committee approved an $8.3 billion military construction bill for 1991 that slashes the president's budget by $837 million, but adds back $208 million cut by the administration to pay for new Army, Air Force and Navy reserve facilities. Included was $1.3 million unrequested by the administration for a joint Army and Marine Corps Reserve aviation facility in Johnstown, Pa., in the congressional district of Rep. John P. Murtha (D-Pa.), chairman of the defense appropriations subcommittee.

The committee also expressed dissatisfaction with Defense Secretary Richard B. Cheney's Jan. 29 moratorium on new contruction contracts, a sore point with members whose districts are affected.