A week after conservatives made major gains in the 1980 elections, the National Conservative Political Action Committee announced yesterday that it has tentatively targeted 20 senators for defeat in 1982.

The new NCPAC target list includes 17 Democrats and three Republicans, and is headed by such well-known Democratic liberals as Edward M. Kennedy (Mass.), Donald W. Riegle Jr. (Mich.), Howard M. Metzenbaum (Ohio) and Paul S. Sarbanes (Ms.).

The list also includes Democrats generally considered more moderate, including Henry M. Jackson (wash.) and Daniel P. Moynihan (N.Y.), as well as Republicans Robert T. Stafford (Vt.), John H. Chafee (R.I.) and Lowell P. Weicker Jr. (Conn.).

NCPAC chairman Terry Dolan said that not all 20 men will end up as targets of the independent conservative organization in 1982. He said the final list will depend on estimates of each senator's vulnerability, the nature of his primary or general-election opposition and whether he moves to the right in the next two years.

If the targeted senators became conservative, Dolan said, they would "automatically remove most of the opposistion" to their reelection.

Pressuring Congress to move to the right was clearly one reason for the early announcement of the target list for 1982. Underscoring this point, Dolan said that the results of last week's election, in which a number of prominent liberal Democrats were defeated and the Republicans gained control of the Senate for the first time in 26 years, represented "a massive conservative mandate."

"Liberals ought to be very intimidated by the mood of the American public," he said.

Under federal election laws, NCPAC and other independent political organizations are able to pour millions of dollars into political races so long as the groups have no contact with the candidates they are backing.In the 1980 elections, Dolan estimated, NCPAC's "independent expenditures" in the six Senate races it targeted totaled $1.2 million.

In four of those races, the liberal Democratic targets -- Birch Bayh (Ind.), John Culver (Iowa), George McGovern (S.D.) and Frank Church (Idaho) -- were defeated by conservatives. The other two NCPAC targets, Alan Cranston (Calif.) and Thomas F. Eagleton (Mo.), survived.

In 1982, Dolan said, NCPAC expects to target more than six races from the list of 20 and to have independent expenditures of more than $2 million. In addition, he said the organization is considering going after key Democratic liberals in the House, including current Majority Leader Jim Wright (Texas), Morris K. Udall (Ariz.) and Phillip Burton (Calif.).

In devising its list of 20 targets for 1982, NCPAC relied on 10 test votes by the senators. According to the organization, senators were "wrong" if they supported the Panama Canal treaties, additional federal aid for New York City, the strategic arms limitation treaty (SALT II) and creation of the Energy Department, and opposed the Kemp-Roth tax-cut bill and the B1 bomber.

Dolan said some of the 20 senators are on the list because "they are extremely vulnerable in primaries, the don't represent their states" and on "key issues they almost always flake off." He cited Democrats Lloyd M. Bensten (Texas), Lawton Chiles (Fla.) and Dennis DeConcini (Ariz.).

Dolan said NCPAC does not plan to play an active role in the selection of Ronald Reagan's Cabinet. Nor will the organization attempt to remove Sen. Howard H. Baker Jr. (Tenn.) as the Senate Republican leader, Dolan said. He called Baker a "bad leader" but compared him with "a drunken distant relative" who could do the new administration little harm.

Other Senators on NCPAC's 1982 target list are Harrison A. Williams Jr. (N.J.), Quentin N. Burdick (N.D.), John Melcher (Mont.), Spark M. Matsunaga (Hawaii), William Proxmire (Wis.), Robert C. Byrd (W.Va.), Jim Sasser (Tenn.) and Howard W. Cannon (Nev.).