A conservative youth group here has been raising money and sending campaign workers to Grenada to help what it calls the "pro-free market, anti-Soviet" New National Party win next Monday's parliamentary election.

"Help finish the job our Marines, Rangers and other brave servicemen started with the historic October 1983 rescue mission," said a Nov. 12 fund-raising letter sent to a few hundred conservative leaders around the United States.

In the letter, former Voice of America official Philip Nicolaides said that without fast action "Grenada could easily fall back into the hands of a socialist government, or, worse yet, an avowed Marxist- Leninist government."

Nicolaides, who left the VOA in 1982 after it was disclosed that he wrote a memo advocating turning the government radio into a hard-hitting propaganda organ, said in an interview that another former Reagan administration official, Morton C. Blackwell, a White House special assistant for public liaison to conservatives, asked him to sign the letter. Nicolaides said he did so after being told the opposition parties were "well-heeled" and "the good guys, the only group that's pro-western, pro-American, pro-free society, is terribly underfunded."

"It would be a finger in the eye to Uncle Sam" if parties led by ousted prime minister Eric Gairy and followers of murdered Marxist Maurice Bishop defeated the New National Party, he said. At stake in Monday's election are the 15 seats in Parliament and the right to form a new government.

Besides the New National Party, the other campaigns are being run by Gairy's Grenada United Labor Party and the left-wing New Jewel Movement that Bishop headed, now called the Maurice Bishop Patriotic Movement.

Headed by Herbert Blaize, the New National Party was formed in August at the urging of leaders from neighboring Caribbean islands who aided the U.S. invasion. A few weeks ago the United States repudiated an ad in which Gairy claimed he had the support of the Reagan administration.

The government pronouncement didn't say whom the administration supported. But a State Department official familiar with Grenada's politics said the administration hopes the New National Party wins the election. "It's nice to see moderates win," he said. "And their campaign has taken off in the last two weeks."

Blackwell said it would not be prudent to discuss the campaign effort until after the election.

Ruth Burns, national political director of Conservative Youth, the project Blackwell set up for the Grenada political operation, said that she went to Grenada three weeks ago to organize the effort.

The Nicolaides letter raised about $2,000, she said. But personal solicitations raised $12,000, enough to send two "political coordinators" to the island, where they are organizing drives to help the New National Party get out the vote.

Burns said her group checked the legality of financing and working in a foreign election before embarking on the venture. "If we represented the New National Party in this country we would have to register as a foreign agent," she said. "But it's okay to work overseas."

The project has no U.S. government backing, she said, although the U.S. embassy in Grenada is aware that her two campaign aides are on the island. "They embassy officials can't be involved, but they have helped us find a place to stay," Burns said.

Blackwell got the idea, she said, in a conversation a month ago with J. William Middendorf II, the U.S. ambassador to the Organization of American States. "He Middendorf said there was a problem down there. He said we the U.S. government couldn't take part in any partisan political activities, but something should be done." Middendorf could not be reached for comment Thursday.

In his fund-raising letter, Nicolaides stressed that the Blackwell political operation in Grenada was "confidential. I'm sure you understand why this must not get into the hands of the liberal media," he wrote. He said later in the letter that the two political coordinators sent to the island would be "keeping a low profile."

Charles McIntyre, a Grenadian businessman who supports the New National Party, said in a telephone interview from the island that he talked with Burns on her visit but has not met the two American campaign workers.

"If they're here, they are keeping a low profile," he said. "They wouldn't like to be publicly identified and we don't like people to be seen as pushing us. We don't want to be accused by the opposition of being pushed by the CIA."

Nicolaides, now executive director of Accuracy in Media, said that Blackwell wanted to keep the campaign effort low-key because the opposition parties might make an issue of the outside help, or some publication might say, "Oh, oh, the right wing is trying to interfere in some country's election," he said.

The project is not intended to interfere in the Grenadian election, he said. "Hardly. I think helping free people -- there's no hint of skulduggery of any kind here -- is the kind of thing we ought to be doing."

Nicolaides said he was concerned that the State Department seems to be so "ultra-fastidious" that it is "sitting on its hands" in the Grenadian election.

"Here in this tiny engagement it would be fairly easy to make sure what was won on the field of battle would not be lost by indifference," he said