With the first phase of its negative advertising attack on Sen. Paul S. Sarbanes (D-Md.) ended, the National Conservative Political Action Committee is turning its sights on Sen. Edward M. Kennedy (D-Mass.), whom it calls the "crowned prince" of liberalism.

John T. (Terry) Dolan, NCPAC's national chairman, said his organization's supporters in Massachusetts will decide next week whether to conduct a test in the Springfield, Mass., television market to see if Kennedy is vulnerable to attacks similar to those that NCPAC credits with defeating four liberal Democratic senators last year.

Kennedy spokesman Robert M. Shrum challenged Dolan's motives, suggesting that NCPAC "needs to claim it's going after Sen. Kennedy because it is useful for their fund-raising." Shrum said NCPAC "has a credibility problem" and would place ads in the Springfield area "to give the appearance that they're really doing something."

Dolan said he is awaiting results of an April 15 survey and fund-raising letter before deciding which other incumbent senators, besides Sarbanes, that NCPAC will target for defeat next year.

The problem with challenging Kennedy, Dolan admitted, is that "while he has a very high negative rating, he also has a very high positive rating. There are a sizable number of people who disagree with him on issues who still will vote for him. The question is, can we convince those people that Kennedy's opposition to everything that Ronald Reagan stands for -- his support for busing, banning prayer in schools and federal funds for abortion -- are more important than their personal liking of him."

A survey of NCPAC supporters found that "on every single issue, Kennedy's on the wrong side. But political legends die hard," Dolan said.

Dolan's letter includes a "confidential ballot" on which respondents are asked to select, from among 21 senators facing re-election next year, five to be targeted. To go after all 21, Dolan wrote, would cost NCPAC $6,540,000.

"I don't mean to imply that we can't defeat all 21. Ninteen-eighty proved there is no such thing as an 'invulnerable' liberal. Once the voters know a liberal's record, he's in big trouble," Dolan said.

Realistically, Dolan indicated, NCPAC could target three to six liberals, including Sarbanes and Kennedy.

Dolan fairly salivates at the prospect of targeting Kennedy, but "to be quite honest, I'd be interested . . . only if I had your [financial] support," he wrote.

Conservatives who are urging NCPAC to target Kennedy, Dolan said, "say, 'imagine what it would mean if we defeated the crowned prince of liberalism in what was considered he most liberal state in the country. That would virtually destroy the liberal movement in America.'"

The strategy behind the early start, Dolan explained, is to "send a shiver down the spine of every other liberal in the Senate. They won't dare oppose President Reagan's politics, if they know they will have to pay the price at the polls."

Meanwhile, in a case of the hunter becoming hunted, a liberal political committee was to launch today a campaign against its conservative counterpart. The Progressive Political Action Committee, calling itself PROPAC, bought space in The Washington Post to attack NCPAC and Dolan.

Another group headed by Pamela Harriman, wife of former New York governor Averell Harriman, already has brought radio time to defend Sarbanes and attack NCPAC and Dolan. PROPAC treasurer Victor Kamber announced the second anti-NCPAC campaign in an ad that quotes Dolan as saying, "A group like ours could lie through its teeth and the candidate stays clean."

Dolan was referring to the fact that candidate's are not legally responsible for the action of independent political action committees of the type he heads. Several candidates whose opponents were attacked by NCPAC in 1980 publicly repudiated its support, saying its negative approach to politics could boomerang.