New York Post publisher Rupert Murdoch's enemies say he wants a newspaper strike. Leonard Saffir's friends say his paper, The Trib, can't survive unless there is a strike.

But neither Murdoch - who is said to want to eliminate the unions to reduce his heavey loses - nor Saffir - whose infant paper, unburdened by union contracts, might gain the readers and advertisers it needs to survive if a strike removed its competition - has as much to say about what choice of papers New Yorkers will have after midnight Thursday as Douglas Lachance.

LaChance heads the Newspaper and Mail Deliverers Union and has emerged as the triggerman in complicated negotiations involving three publishers and 10 unions. All of which have contracts that expire this week.

In an age in which publishers Of The Post, The New York Times and Daily News have trained nonunion executives to run equipment that could keep the papers publishing without union employes, LaChance's truck drivers are the key.

"The most difficult thing for the publishers is to get the thing delivered, not to produce it," H.J. Kracke, executive director of the Publishers Association, which represents The Times, News and Post, said in an interview.

LaChance has proclaimed that his union will take the lead in negotiations, and spokesmen for other unions counselled: "Don't watch us for a while, watch the drivers."

Watching LaChance and his drivers is easier said than done. His union has traditionally been happy to deliver one paper while striking another. During the 114-day 1962-1963 strike, LaChance's union delivered The New York Standard, a paper written largely by strikers from other papers which made a million dollars during the strike for its three founders, one of whom was Leonard Saffir.

LaChance said early that he will not negotiate past the Thursday midnight deadline with the Daily News, with which the drivers have had numerous run-ins in recent years.

In a caustic letter to the News, LaChance noted that the paper's editorial page called his men "$500 a week truckdrivers" and said he would make that wage his goal in contract talks. His drivers make $332.26 a week although overtime pushes them close to $500, LaChance said.

While seeking a confrontation with the New LaChance offered The Post and Times separate negotiations and The Post accepted. The unity of the Publishers Association which is negotiating jointly with the other nine unions is unbroken by The Post's defection, publishers' representatives insist.

In fact, workers and publishers know that Murdoch is losing more than $150,500 a week with The Post and that this paper is too fragile to be exposed to a strike. "I thought it was in our best interest and theirs for The Post not to get tied up with the News," LaChance said.

While LaChance is angry at the News, officials of another union, The Newspaper Guild, are angry at Murdoch.

The Guild representing newsroom and commercial personnel, is in a volatile position. "We now have in this city three nespapers all employing something like twice as many people as they need . . . all paying them rates of pay, with the exception of the better journalists, well beyond what the market can bear," Murdoch recently said in praise of The Trib's freedom from unions.

Although The Times, News and Post are bargaining jointly, only The Post has put forward what The Guild calls "the Auschwitz clause."

"We're on a collision course," said Harry Fisdell, executive vice president of The New York Guild.

What Fisdell calls the Auschwitz clause would give Murdoch the one-time right to fire all post staff members "incompatible with the new management's publishing concept."

A one-time volley of firings would be enough, Post editorial employes believe to destry their union. Post management has been asking employes to quit The Guild arguing that they will be out of The Guild sooner or later so they might as well resign now and work during the strike.

"What's ominous is that the management people talk about a strike as though it's a given," said a Post reporter.

The 450-member Guild unit at The Post makes clear that it will work past the strike deadline as it has in the past, but many post employes fear that Murdoch will try to force a strike. "Maybe he can get one if he's beastly enough," one said.

Over the weekend, Post executives practiced putting out a paper without union employes. The dry run, they said, was not meant to intimidate employes nor was it a violation of their labor contracts.

The executives were trained in Oklahoma City at Southern Production Program Inc., which is designed to prepare newspapers to publish without their union employes. The Washington Post used some employes rrained in the same school to help put out its paper during a pressmen's strike in 1975.

In addition to the "Auschwitz clause" at The New York Post, The Guild is fighting a proposal by the managements of all three papers to remove about 20 percent of Guild employes from the union's jurisdiction. Similar proposals have triggered prolonged bargaining at other newpapers, including The Washington Post.

Under the publishers' proposals, about 400 of the 2,100 Guild workers at The Times, 200 of the 1,350 Guild workers at the News and 100 of the 450 at The Post would no longer be covered by the union.

For its part, The Guild is asking 20 percent wage increases across the board at the News and Times and 25 percent at The Post, which lags 5 percent behind the others at present.

New York's newspaper industry hs a bitter history of labor negotiations. Ten strikes have halted publication since 1950, the most devastating in 1962-1963 and 1965.

Estimated losses to the newspapers, unions and businesses from the 1962-63 strike ran between $190 million and $250 million. Retail stores, theaters, museums and amusements suffered without newspapers to list their their sales and attractions.

The Mirror, Journal-American, World-Telegram and Sun, Herald-Tribune, Long Island Press and Long Island Star-Journal were all publishing then and noen remains.

Saffir's Trib started in January but has failed to make headway against the morning competition of the News and Times. It prints about 150,000 copies daily although it sells fewer than 100,000, but saffir said production can "go up to whatever we can sell" in the event of a strike. If there is no strike, many observers believe, The Trib may be doomed.

If Times News and Post were shut down, The Trib's only New York competition would come from News World, a paper published by the Rev. Sun Myung Moon's Unification Church. Larry Moffitt, a spokesman for News World, said his his paper would increase its press run but refused to say what the present circulation is.

Ray Shaw, The Wall Street Journal's executive vice president, said The Journal would be likely to increase its south Brunswick, N.J., press run somewhat. The Journal is not affected by the current labor negotiations. It prints 245,700 copies daily in South Brunswick.

During past newspaper strikes, papers from Newark, Philadelphia, Boston and other cities have been snapped up when they reached New York newsstands.