Prospects for any quick settlement of New York's week-long newspaper strike were dealt a blow yesterday when the Newspaper Machinists' union voted unanimously to authorize its own strike against the city's three major daily papers.

The 300-member union has been honoring picket lines at the Times, Post and Daily News that were set up after the Printing Pressmen's Union went out on strike Aug. 9. Yesterday's vote by the machinists would enable them to collect strike benefits, which are available only when the union has called a walkout.

"We'll put up a picket line when we feel it is appropriate," said Richard Hubert, business agent for the machinists.

Charles McNalley, executive secretary of the Allied Printing Trades Council, which represent all nine of the newspaper craft unions here, said a strike by the machinists is likely if the pressmen's strike isn't settled this week. McNally predicted that similar strike authorizations would be voted soon by the paper handlers' and electricians' unions.

Only one of the unions, the typographers', has a contract with the newspapers. Contracts for the other unions expired last March 31.

The strike vote by the machinists and other unions could further complicate what is already a complex negotiating puzzle surrounding the pressmen.

Newspaper officials have sought to cut back the number of pressmen assigned to printing presses, claiming they are no longer needed because of automation and the simplification of the printing process.

The pressmen claim that the manpower reductions sought by the newspaper owners would badly cut into the number of jobs available to the union's membership, and that the new technology should require additional employment of union members.

Both sides have warned that negotiations could be difficult and that a long strike may be in store for the city's papers. The last major strike to hit New York's newspapers went 114 days through 1962 and 1963 and eventually cost the city four of its papers.

Union officials and others involved in the current negotiations said yesterday that strike votes by the additional craft unions could stretch out any walkout since it would mean additional contracts to be negotiated and a possibly tough bargaining position by the individual unions.

New York officials have estimated that the strike has been costing the three papers upwards of $2 million each day as well as readership in critical suburban areas.