Sen. Robert C. Smith, a conservative New Hampshire Republican who quit the party last July on grounds that it had drifted too far left, replaced Sen. John H. Chafee yesterday as chairman of the Environment and Public Works Committee.

Smith, who had folded his independent campaign for president, rejoined the Republican Party on Monday — eight days after Chafee's death opened the powerful chair — and declared his interest.

In a move that alarmed but did not surprise environmentalists, the Senate Republican Conference elected Smith yesterday afternoon by 32 votes, to 4 votes for Sen. James M. Inhofe of Oklahoma, another staunch conservative who disagreed with Chafee on most of the major conservation issues.

Smith declined to answer any questions about his plans for specific legislation before the committee, refusing to say, for example, whether he will fight for the compromise extension of the Superfund hazardous waste law that he and Chafee had worked out.

But Smith said that "people who have prejudged me" as a foe of environmentalism "may find that they have done that prematurely."

"It's a sea change," and not for the betterment of the environment, Sen. Jack Reed said of Smith's elevation. "Senator Chafee was a committed environmentalist who always tried to seek a balance between environmental policy and economic development."

Reed said Smith "sees the environment as sort of a hindrance" to the goals of business and industry. "The whole demeanor and the whole agenda of the committee is going to change now," he said.

Still, Reed said Smith will be somewhat more sympathetic to the environment than Inhofe would have been. "He's from New England and does at least have some of our sense of the importance of the environment," he said of Smith.

Mike Casey, a spokesman for the Washington-based Environmental Working Group, predicted that under Chairman Smith, "the Clean Air Act is going to come under much more pointed attack" than Chafee would have permitted.

Reed and Casey were among those who said yesterday that Chafee was forced to devote much of his power as chairman to blocking anti-environmental legislation that his more conservative GOP colleagues sometimes had the votes to pass. As chairman, he had the power to set the agenda and, generally speaking, to decide whether to call a vote on a bill.

Senator-designate Lincoln D. Chafee will all but certainly be granted his preference for a seat on the committee his father led for the past five years. But environmentalists noted that, as the most junior member of the 10-Republican, 8-Democrat panel, Chafee will have comparatively little influence.

When he left his party last summer, Smith avoided criticizing his Senate GOP colleagues — a mark of respect for the collegial Senate traditions that probably permitted him to assert his seniority claim to the chairmanship.

But he was blunt in his attack on the party at large, which he considers to have given up on such principles as opposition to abortion. "This is not a party," he said in July. "Maybe it is a party in the sense of wearing hats or blowing whistles, but it is not a political party that means anything."

Smith ranked below Sen. John W. Warner, R-Va., in committee seniority but Warner would not give up his Armed Services Committee chairmanship to take Chafee's place.

Inhofe, who ranks one slot below Smith in committee seniority, had hoped he would get the job because of Smith's defection to the independent ranks. But Warner, with Lott's blessing, stepped in as a broker to prevent what Smith called a possible "bloodbath" in the party.