MINNEAPOLIS (AP) _ Negotiators for Northwest Airlines pilots said Wednesday a strike is possible by Labor Day, but Los Angeles investor Alfred Checchi said the strike threat won't stop him from completing a takeover of the nation's fourth- largest carrier.

Negotiators for the Air Line Pilots Association told leaders of Northwest pilots Tuesday night that a breakdown in contract talks ''may be near.''

But they also said that agreement on a new contract could be reached ''within a matter of hours'' if NWA Inc. management would bargain in a reasonable and responsive manner.'' NWA is the parent company of Northwest Airlines.

A spokesman for Northwest did not immediately return a phone call Wednesday.

Meanwhile, the Northwest pilots Master Executive Council of ALPA stopped short Tuesday night of endorsing Checchi's $4 billion plan to buy NWA.

''They stopped short of a complete endorsement of his buyout plan, but judged his financial and business plans to be viable,'' union spokesman Jim Halverson said Wednesday.

Earlier Tuesday, former Republic Airlines pilots now working for the Eagan- based Northwest embraced Checchi's $121-per-share takeover bid.

Halverson said the mediated contract talks were set to resume Wednesday afternoon. Remaining issues are job security, work rules and pay, he said.

Before a strike could occur, an impasse in contract talks would have to be decided by the National Mediation Board. If an impasse were declared, it would be followed by a 30-day cooling-off period, after which the pilots would be free to strike.

Checchi said Wednesday his group intends to close the buyout deal despite the strike threat. He said he considered the actions by the Republic and the Northwest Master Executive Council on his buyout plan ''very encouraging.''

He also said he didn't know when the deal would be completed, but it was ''pending very shortly.''

Last week, sources close to the transaction said Checchi expected to complete the deal before Aug. 1, the St. Paul Pioneer Press Dispatch reported Saturday. The Star Tribune, also quoting unidentified sources in its Saturday edition, said Checchi might close the deal by Friday.

Checchi also said Wednesday that a contract settlement might be reached before the deal is closed.

''These pilots and the company have been involved in negotiations for almost two years and that process seems to be coming to a satisfactory conclusion,'' he said. ''It's my understanding they're very close and, sometimes when you get closest, it's kind of a point of maximum frustration for both sides.''

Former Republic Airlines pilots who joined Northwest in the acquisition of Republic in 1986 have been without a contract for the past 2 1/2 years while the contract covering Northwest pilots expired three years ago.

Talks to bring the pilots under one pact began in April 1987 and broke off last November, when 96 percent voted to authorize a strike. Northwest then requested federal mediation and the talks resumed in December.

Northwest spokesmen said last week that, as long as talks continued, an agreement was possible.

But in the ALPA statement issued Wednesday, pilot leaders expressed ''increasing impatience'' with the lack of progress in contract talks and said a breakdown ''seems inevitable if talks aimed at a new contract do not produce an agreement within a matter of days.''

As for the Checchi buyout plan, Halverson said Northwest pilot leaders ''had some difficulty in divorcing an endorsement of the Checchi buyout proposal from a lack of progress in contract negotiations.''

''He (Checchi) has been saying it's a done deal. On the other hand, he says he has little or no influence in contract negotiations,'' Halverson said. ''And we're saying it's difficult to reconcile those two statements.''

Checchi said Wednesday he doesn't own the airline and, therefore, it ''would be totally inappropriate for me to be involved in contractual negotiations of an enterprise that I don't control.''

Halverson said Northwest pilots are concerned about the ''large debt load'' in the buyout offer. ''That's a problem for all pilots,'' he said.

The Northwest pilots, however, did conclude that the buyout plan ''appears viable'' from a business and financial standpoint. The Northwest group passed a resolution saying it endorses the Checchi group's ''stated intentions for market growth, expanded employment opportunity and the promise of harmonious employee-employer relations.''

The Republic Master Executive Council called Checchi's proposal the best available option to provide ''stability and growth potential'' for NWA and its workers.

But union spokesman Curt Kruse said Tuesday that former Republic pilots' endorsement of Checchi's buyout offer doesn't mean pilots are pleased about the pace of contract negotiations. He also stressed that the pilots still have concerns over the debt Northwest would incur.

''Nobody is entirely pleased with increasing the debt at Northwest,'' Kruse said. ''However, once we had an opportunity to review his (Checchi's) financial plan, our concerns diminished somewhat. We still have concerns.''

The Northwest MEC represents about 3,000 of the total 5,000 pilots employed by Northwest. The rest are represented by the Republic Airlines MEC.