The financially troubled New York Daily News today officially dropped the United Press International news service, depriving UPI of a vital source of income, but the news tickers continued to run at the paper as UPI hoped for a reprieve.

Daily News editor Michael J. O'Neill said that UPI agreed to continue its service "at no obligation to the paper" in hopes that further talks would result in revival of a contract that the tabloid allowed to lapse last December.

Roderick W. Beaton, UPI president, said he expected negotiations to go on "for some time."

A Daily News executive said the tabloid pays UPI about $55,000 a month for news wire and photography services. UPI has about 1,900 employes and 7,500 customers for its news, photo and radio services.

UPI, which has been up for sale for more than two years, is 95 percent owned by E. W. Scripps Co. of Cincinnati and 5 percent by Hearst Corp. Reportedly unprofitable for 25 years, it lost about $4 million in 1981 and in 1982 expects losses of about $3 million, not counting the effect of losing the Daily News as a client.

Meanwhile, the fate of the Daily News remains uncertain.

New York real estate entrepreneur Donald J. Trump was expected to announce a plan to acquire the newspaper, which was put up for sale on Dec. 18 by its parent, the Tribune Co. of Chicago.

Other candidates to acquire the newspaper, which lost $11 million last year, include former Washington Star owner Joe L. Allbritton and John L. Dyson, chairman of the New York Power Authority.

Any offer for the Daily News will hinge on concessions from the paper's 13 unions representing about 3,800 full-time employes.

Among the concessions that all the buyers see as necessary, according to sources involved in the negotiations, is the elimination of some 1,500 jobs.