Ever since Horace Greeley's 125-year-old New York Herald Tribune died in 1966 from terminal competition, would-be publishers have been dreaming the impossible dream of starting up big new newspapers in Metropolis.

John M. Shaheen, the oil refinery millionaire, announced in the spring of 1973 that the New York Press would make its debut from the printing plant of the old Morning Telegraph on West 52d Street.

Further christenings were announced for the autumn of 1973, the spring of 1974, the end of 1974, January of 1975, April of 1975, the summer of 1975 and the end of 1975. Finally, Shaheen announced there would be no more announcements until the paper came out.

Next came the Rev. Sun Myung Moon's entry into the market, the News World, which recently established something of a precedent in the publishing industry by lowering its newsstand price from 25 cents to a dime while simultaneously lowering its advertising rates. It could do that, presumably, because of subsidies from Moon's Unification Church.

Many of its street corner hawkers now give the News World away, and one Moon disciple passes out the paper on Fifth Avenue and 50th Street while at the same time playing the Battle Hymn of the Republic on a Sousaphone.

Against this backdrop of high-drama publishing competition, another new daily newspaper is scheduled to hit the stands this fall. But for the first time since New York boasted 13 dailies after World War II, there appear to be the ingredients for success and a revival of the kind of morning newspaper competition that once made New York the communications capital of the world.

Backed by investments by former Treasury Secretary William E. Simon and former U.S. Sen. James L. Buckley, The Trib, a tabloid-sized morning paper, is scheduled to start up this fall with an initial circulation of 200,000 to 300,000.

Leonard Saffir, an ex-aide to Buckley, and John Denson, former editor of the defunct Journal American and Herald Tribune, as well as an editor of Newsweek magazine, are creating what they say will be a serious paper that will be moderate to conservative in ideological bent and private a balance to the New York Times and Daily News in the morning field.

"It's not going to be an ideological puff sheet, I can assure you of that," said Saffir, who was Buckley's chief assistant until the Conservative Republican senator was defeated in the November election.

Simon, too, said The Trib will not become a conservative house organ. "I don't believe in papers that tilt one way or another. It's going to be moderate," he said recently.

Simon, who said he invested a "moderate" amount of cash of finance the prototype, said. "I believe this is an idea whose time has come." He said he would help find investors for The Trib, but htat he does not have time to write a column for it.

Saffir, who will serve as publisher and own controlling interest in the venture, said the tabloid format was geared to the commuter market in the New York, New Jersey and Connecticut suburbs, but that The Trib will mix its national and international reports with New York City news and will "fight like hell for the financial survival of this city."

He said financial backing has been pledged by about a bozen investors from Wall Street, California and Texas, some of whom are friends of Buckley and Simon, both of whom are on the board of directors of the paper.

Saffir, in an interview, declined to disclose the startup cost, but said it will be in eight figures, or at least $10 million. He declined to identify the other backers.

Saffir said The Trib has signed a 10-year, $4 million lease for office space on Third Avenue, near the Daily News building, and will have a 72-page prototype of the new newspaper for use in generating advertising.

The pilot edition includes political stories by former New York Times and New York Magazine reporter Richard Reeves, who will be a Trib contributor, and by Warren Rogers, formerly of the Washington bureau of the Herald Tribute and currently editor of the yet to be published Washington Journal Review.

A number of other Herald Tribune writers will work for The Trib, Saffir said, including art editor Emily Genauer and ex-Herald Tribune crossword puzzle editor Ruth Biemiller.

The Trib, whose name is the same as the popular abbreviation for the Herald Tribune, found itself in a copywright dispute with the publishers of the Paris-based International Herald Tribune, but Saffir said the challenge has been dropped. The International Herald Tribune is owned jointly by The Washington Post, The New York Times and Whitney Communications, Inc.

Saffir dismissed suggestions that The Trib could face the same startup difficulties that Shaheen did, claiming that comparisons between the two ventures are impossible to draw.

Saffir noted that Shaheen was an oilman who decided to get into the newspaper business and reportedly lost his financial backing while his oil refineries in Newfoundland were going out of business.

Shaheen poured an estimated $25 million into his project, chartering the Queen Elizabeth 2 to take scores of advertising executives on two junkets to Bermuda. The trips were hailed as success, but the New York Press is "waiting for an economic upturn" before its first issue is offered, a company official said with a straight face recently.

"He went out and bought presses and started importing expensive marble for his building before putting together a concept for the newspaper. We're not doing that," Shaffir said.

The Trib, he said, is being conceived, nursed and massaged right along by professional news people.

Saffir, 46, ran a paper called the New York Standard here during the long newspaper strike of 1962 and 1963, befire which he was a correspondent for the Hearst newspapers. In 1965, he started the Latin American Times, a now-defunct paper which provided South American news to American businessmen.

Denson, who is 73, has most recently been teaching journalism in New York and doing free-lance writing while in semi-retirement. Besides being editor, he is a stockholder in The Trib.

Saffir said the new paper will not invest in a printing plant, instead contracting out to an out-of-town printer. The newspaper will be put together in New York with computerized equipment linked to the contract plant, where page composition and offset printing will be done, he said. The Monday-to-Friday paper will then be trucked to its circulation areas.

Saffir said The Trib has signed on with the Tinker, Campbell-Ewald adagency, which handles the General Motors and Coca-Cola accounts, and has already received commitments for yearly contracts by numerous national advertisers.

He said the editorial staff of The Trib will number about 100, with approximately 75 business and advertising employees.

If The Trib is successful, it will intensify an awakening of New York newspaper rivalry that began earlier this year with Australian Rupert Murdoch's purchase of the faltering New York Post, whose afternoon circulation claims have since been increased from 489,000 to 619,000.

The Times weekday circulation is 870,000 and the News is 1.9 million.

The backers of The Trib say now that the morning market is wide ipen, and that they can provide an alternative to The New York Times while filling a daily hard new04s void in The Wall Street Journal.

"We're not going tobe flashy and splashy, but we're going to appeal to people who want to read a morning tabloid. We think we have a way of putting some life back into the morning competition," Saffir said.