Democratic Party officials yesterday pruned the once rosy fund-raising estimates of their weekend telethon, citing what one official called "an unanticipated number of hoax calls and jamming calls."

But they say they believe they will still show a profit of at least $1 million and perhaps as much as $3 million.

Party spokesman Robert Neuman said that a check of the telethon's computerized records showed that eight critical and hoax calls were received for every two or three good calls.

Many callers supported President Reagan and criticized the Democrats, he said. But many others posed as legitimate supporters, and pledged contributions using such names as Jimmy Carter and Rosalynn Carter.

With a few telephone banks still not tabulated, records show at least 150,000 genuine pledges, averaging $85 each, for a total of almost $13 million, Neuman said. Generally, half of such pledges are fulfilled, he said, and this time officials expect a higher return.

If half of the pledges are fulfilled, the telethon will bring in more than the $6 million it cost. A return of more than 60 percent could mean a profit of $3 million. Earlier, telethon officials claimed $20 million in pledges.

"We just didn't anticipate the fraud factor--the bad calls," Neuman said. "But without question this still was an unqualified success."

Actually, the telethon benefited from a public relations bonanza, courtesy of the Republican National Committee, with an assist from the Moral Majority.

For weeks, Democrats had fretted that their telethon was generating no publicity and would be a fiscal disaster. But just when the Democrats seemed to be up to their line of credit in malaise, along came GOP Chairman Frank Fahrenkopf.

He sent a letter to almost 1 million Republicans, warning that the telethon would be a "smear campaign" against the president by "Hollywood left-wingers" and "liberal kingpins"--and asking them to call the telethon to protest.

Democratic Chairman Charles T. Manatt quickly charged the Republicans with a "dirty-tricks" effort to sabotage the telethon by jamming the phone lines. He threatened to sue, and spent the next week pounding this theme in the media.

"We're milking this for all it's worth," conceded one Democratic strategist. "It's the best thing that could have happened to us."

Meanwhile, Moral Majority officials were so moved by the GOP letter that they did a minor re-writing of it and sent the same appeal out to 100,000 of their own supporters. The appeal was signed by the Rev. Jerry Falwell.

"We just didn't have time to try to re-invent the wheel," said Dr. Ron Godwin, of the Moral Majority, explaining why the two letters were so similar. "Why try to improve on a good thing?"

Asked if the GOP had urged his group to act, Godwin said: "There was no intercourse of information at all."

A number of callers were rude and lewd, said Ursula Opalinski, executive vice president of the National Switchboard, which ran two of the phone banks.

She said many callers were so abusive and obscene that several operators left in tears.

"We handle a lot of different telethons, religious and diseases and the rest, but we've never had one like this," she said. "This one brought out the ugly."