Lincoln D. Chafee, son of the late Sen. John H. Chafee (R-R.I.), was chosen yesterday to fill out the remaining 14 months of his father's term, boosting Republicans' hopes of retaining the seat and preserving their Senate majority in next year's elections.

Chafee's appointment by Rhode Island Gov. Lincoln Almond (R) came as Sen. Robert C. Smith (R-N.H.) was chosen to succeed the elder Chafee as chairman of the Senate Environment and Public Works Committee, signaling a significant change in its direction. Chafee, a moderate, was known as one of Congress's leading environmentalists, while Smith is a conservative noted for his pro-business, anti-regulation outlook.

Lincoln Chafee, 46, is the mayor of Warwick, Rhode Island's second-largest city, and, like his father, a political moderate with a record of working across party lines. He had already announced he would be a candidate to succeed his father, who decided last spring to retire at the end of his term next year. The senior Chafee, who was 77, died Oct. 24 of heart failure.

Republicans said Lincoln Chafee is likely to be sworn in today or Thursday. They also said he will be appointed to the environment committee, but his father's seat on the powerful Finance Committee will go to a more senior Republican.

In a brief statement, Chafee signaled his intentions to carry on in his father's tradition. "I do realize that a high standard has been set, and I look forward to carrying on in the tradition of excellence that the people of our state have come to expect and rightfully deserve," he said.

In accepting the appointment, which came as no surprise, Chafee took on the advantages of incumbency, which are often strong in a small state such as Rhode Island. But Rhode Island is also heavily Democratic, and Chafee could face some difficult votes next year that could complicate his campaign.

Republicans insisted it was all a plus. "He goes from being an underdog to being a likely winner . . . it really changes the whole dynamic," said Sen. Mitch McConnell (Ky.), chairman of the National Republican Senatorial Committee. "There are no minuses."

Democrats argued that they still have the advantage of experienced, well-known Democrats running in a Democratic state: Rep. Robert A. Weygand and former lieutenant governor Richard Licht, who are vying for the party's nomination. Also, Chafee "is going to have to cast votes with a very conservative [Republican] majority that are often at variance with the interests of Rhode Island," said Democratic Senatorial Campaign Committee Chairman Robert G. Torricelli (D-N.J.).

Republicans said they expect the younger Chafee, like his father, to stray from the party line when conscience and politics dictate and suggested that he may get a "pass" next year on issues that could cause him trouble back home.

Chafee is the first son to be chosen to fill out his father's term in the Senate since 1965, when Harry F. Byrd Jr. of Virginia was tapped to succeed his ailing father. A former blacksmith at harness race tracks in the United States and Canada, Chafee worked for several Rhode Island businesses before running for the Warwick city council. He won four successive terms as mayor of the heavily Democratic city.

Smith, who returned to the GOP Monday after bolting earlier this year with a withering blast at the party for abandoning conservative principles, was chosen to head the environment committee after Sen. James M. Inhofe (R-Okla.) dropped out of the race.

Inhofe, another conservative who was next in line behind Smith, said he stepped aside to avoid a "bloodbath" and because Smith had the edge in seniority. But some Republicans were still angry at Smith, and the vote by GOP senators to ratify Smith's nomination by committee Republicans was 32 to 4.

CAPTION: Lincoln D. Chafee, left, with Rhode Island Gov. Lincoln Almond after being named to his late father's Senate seat.