Union leaders at the Daily News voted unanimously today to offer to buy part or all of the morning tabloid's stock to rescue the 1.5-million-circulation newspaper from a possible shutdown.

The heads of 11 unions representing 3,800 employes authorized labor lawyer Theodore W. Kheel to open negotiations with Tribune Co. of Chicago, owner of the News.

Kheel, serving as temporary trustee of the News Employes Stock Ownership Trust, previously set up as a last-resort purchaser of the paper, announced later that Tribune Co. representatives had agreed to a meeting Thursday in New York.

Meanwhile, it was revealed today that the News, in a cost-cutting measure, informed United Press International last week that it was dropping the news service at the end of this month.

And another failing publication, the afternoon Minneapolis Star, will be merged into the morning Minneapolis Tribune, their publisher said today in an announcement to the staffs that had been expected.

Following an $11 million loss last year by the Daily News, Tribune Co. has sought a purchaser for the paper, with the implication it may close the paper if no buyer is found. A number of potential purchasers have looked at the paper, but with little word on whether any are interested.

George E. McDonald, president of the Allied Printing Trades Council, called the union leaders into an emergency meeting after Tribune Co. President Stanton R. Cook wrote to Deputy Mayor Karen E. Gerard, declining an offer of aid in financing a new or refurbished automated printing plant for the News outside the high-priced Manhattan real estate area.

The purchase offer "does not represent a change in the basic position of the council" that the trust "should be a buyer of last resort," McDonald said, emphasizing that the trust "will step aside for any other responsible buyer interested in acquiring all of the stock of the Daily News.''

McDonald also said the trust "will also be ready to enter into a joint purchase agreement with any buyer so desiring."

Neither Kheel nor McDonald would discuss the size of the purchase they had in mind, explaining that it depends on what sort of package might be involved. The News Building and attached property in Manhattan alone could represent $100 million if included in a sale of the News, the nation's largest general interest daily.

Kheel said the labor group could raise more than $6 million over the next 12 months if workers put in escrow the $36-a-week pay raise due next week.

In addition, he said, it could raise money through loans from union pension funds and tax benefits totaling as much as $50 million.