The National Conservative Political Action Committee, the bad boy of American politics during the last two elections, has switched tactics this fall.

Gone are the "hit lists" of liberal House and Senate members that made NCPAC famous. And the massive negative advertising campaigns against targeted liberals have all but disappeared.

Instead, NCPAC is spending the bulk of the $14 million it has raised in the last two years on positive advertising to get President Reagan reelected. It has launched an "American Heroes for Reagan" campaign, a voter-registration drive among conservatives and a "blacks for Reagan" program.

However, NCPAC has not abandoned the hard-hitting negative attacks that made it one of the most controversial groups in American politics. The headline on a NCPAC brochure prepared for distribution in black communities, for example, says: "Walter Mondale wants to keep you in your place; Ronald Reagan wants you to own your place."

After plugging an urban homestead act supported in the Republican platform, the brochure concludes: "Walter Mondale believes that happiness is a government handout in a welfare state where black people are treated as . . . wards of the government. Ronald Reagan believes that pride is found in private ownership in a free land."

NCPAC has contributed about $200,000 in cash and services to 130 House and Senate races this year. But it is running only two major independent-expenditure campaigns this fall, according to Communications Director Craig Shirley. The largest is a $2 million effort directed against the Democratic presidential ticket of Mondale and Geraldine A. Ferraro.

The group has produced six television commercials lambasting the Mondale-Ferraro ticket, including one featuring an attack on Ferraro by Anne M. Burford, who was forced to resign as administrator of the Environmental Protection Agency.

"Remember how bad things were under Vice President Mondale," says another advertisement. "Just imagine how bad things would be under President Mondale."

NCPAC is also running radio and television ads in Iowa that accuse Democratic Rep. Tom Harkin, who is challenging Republican Sen. Roger W. Jepsen, of voting to "give away the Panama Canal" and of being "too liberal for Iowa."

The $50,000 that NCPAC is spending in Iowa is a far cry from its efforts in other recent elections. In 1982, for example, it spent more than $175,000 in each of eight Senate races, including $664,610 in an unsuccessful attempt to defeat Sen. Paul S. Sarbanes (D-Md.). Only one of NCPAC's major targets in 1982, Sen. Howard W. Cannon (D-Nev.), lost, leading Democrats to claim that NCPAC had lost its clout.

Shirley said the decision not to issue "hit lists" or target liberal congressional candidates this year had nothing to do with 1982 losses. "We're almost a victim of the success of the conservative movement," he said in an interview in NCPAC's new offices in Alexandria. "There simply is a lack of high-profile liberal Democrats up for reelection this year."

Mark Johnson, press spokesman for the Democratic Congressional Campaign Committee, disagreed. "They don't have the money anymore. NCPAC is a financial disaster," he said. "They simply aren't the force they once were."

Shirley said 1984 has not been as good a fund-raising year as some conservative organizations had hoped. Nevertheless, he said NCPAC has had a "fantastic year" raising $14 million during the election cycle.

"Walter Mondale is hard to raise money against because our contributors don't take him seriously," Shirley said. "We all would have done better if the presidential race would have been closer."

"Things have come full circle. We used to raise money by attacking liberals," he said. "Now liberals are raising money attacking NCPAC in races we're not even involved in."

Meanwhile, NCPAC has had a lower profile than in recent elections. Shirley said the group's chairman, John T. (Terry) Dolan, "wouldn't want me to say this, but we're starting to look like the establishment."