Sen. John G. Tower (R-Tex.) stood up for a big beach-front developer on the Gulf coast. Sen. Howell Heflin (D-Ala.) went to bat for a beach owner in Florida. Rep. Walter B. Jones (D-N.C.) looked out for friends around Cape Hatteras and Rep. Trent Lott (R-Miss.) for an island owner off Mississippi.

Their good works occurred in the final hours before Congress recessed last week, as these and other legislators refined the Coastal Barrier Resources Act, a major but deceptively named environmental bill.

Once they were done with it the bill, watered somewhat by exemptions that could assure millions of dollars in future profits to coastal land owners, was easily passed and readied for President Reagan's signature.

Regarded as the most important environmental protection to emerge from this Congress, the barriers bill is designed to slow -- or stop -- commercial development on about 700 miles of fragile, mostly untouched coastal barrier beaches and islands.

Rather than prohibit development on these shifting and sometimes dangerous strips, Congress took a different tack. The legislation bars property owners from receiving federal financial assistance, ranging from home and sewer loans to road-building grants and federal flood insurance.

"Those who own property on undeveloped barriers have the option to build and develop as they wish -- but at their own financial risk, not at the risk of U.S. taxpayers," explained the chief sponsor, Sen. John H. Chafee (R-R.I.), as the bill moved through the Senate.

About 40 percent of the nation's existing 2,500 miles of barrier shoreline is developed or being developed; 47 percent more is undeveloped but protected. The remaining 13 percent, to which the bill applies, is undeveloped and unprotected. The potential for commercial and residential development of those areas is enormous.

Virtually all are magnets for investors and many are ticketed for development in the distant future. "We're talking megabucks here," said a Chafee aide.

Interestingly, Chafee owns a residence in one of those unprotected areas in his home state. He made certain that the final bill included the Card Ponds barrier area, even though the Department of the Interior recommended that it be exempted. Result: Chafee and his neighbors are now banned from receiving any federal aid if they intend to expand or develop.

Such restraint was less evident elsewhere in the House and Senate as a phalanx of lawyers, lobbyists, developers, mayors and town councils hammered at their legislators, seeking exemptions from the development-aid ban working its way through congressional committees.

"Isn't it curious how these changes occurred?" said Ric Davidge, who headed an Interior Department task force that drew up the first proposed list of areas to be covered by the legislation. "But don't ask me. Ask Congress how it happened."

Davidge's task force proposed about 750 miles of barrier shoreline for the new protections. The House and Senate versions covered lesser amounts, but by the time the measure emerged from conference committee last week it included an estimated 700 miles in the ban on federal development aid.

The largest chunk excised from the bill was a 7 1/2-mile stretch of nearly pristine beach on South Padre Island along the Texas coast, owned by the American General Investment Corp., a Houston development firm.

American General officials earlier this year wrote to Interior Secretary James G. Watt, protesting his department's designation of the strip for inclusion in the protection package.

"Unfair to private property owners," American General wrote. "The true motivation . . . is anti-development, anti-growth, political-environmentalists who prefer to stop all growth along our coastline."

But Watt wouldn't budge. Sen. Tower wrote to Watt twice, urging a new look and full review of the facts. Watt still wouldn't budge. Chafee wouldn't budge either, leaving the South Padre Island strip in his Senate bill, even though American General contended it already had spent $6 million to begin development of 730 of the 21,000 acres it owns on the barrier.

When the measure emerged from the House Merchant Marine and Fisheries Committee, however, it came out without the South Padre Island provision. According to committee aides, Tower and Rep. E (Kika) de la Garza (D-Tex.), the area's congressman, had helped persuade House members to give American General a hand.

Something similar occurred with the Usinas Beach unit, a St. Johns County, Fla., beach-front tract owned by B. F. Goodwin, a Birmingham constituent of Sen. Heflin. The senator argued that substantial development had occurred there already, but neither Interior nor Chafee could find it in their aerial photos.

They held firm, insisting that Usinas Beach be included in the bill. But Merchant Marine and Fisheries, sources said, bowed to Heflin's protests and removed the area from its version of the bill. It stayed out of the final bill as well.

Florida's Rep. Bill Chappell Jr. and Sen. Lawton Chiles, both Democrats, took up the cudgels for a tract in Chappell's northeast Florida district, some five miles of shoreline designated as the Guana River unit. That, too, although on Interior's original designation list, was removed by the time it left the House.

"Florida probably has more barrier coastline than any other state, so there was considerable interest in this issue," a Chiles aide said. "But we felt the definitions of 'development' were not clear. We adopted the ombudsman's role as we always do and passed along information about Guana River to Interior and to the committees."

Walter Jones, chairman of the merchant marine committee, joined with North Carolina Republican Sens. Jesse Helms and John P. East in arguing to exempt three previously designated units in their home state. They prevailed. So did Trent Lott, the House minority whip, calling for exemption of a Gulf coast unit called Cat Island.