New York state could face s shutdown of its five nuclear power reactors in August if it does not clean up a political tangle over emergency preparations, the Nuclear Regulatory Commission announced yesterday.

In related matter, Ralph Nader's Critical Mass Energy Project called yesterday for the shutdown of 20 reactors that are operating or are under construction at 11 sites around the country because they have "adverse population density," or too large a population nearby, according to an NRC study.

The NRC classified all the nation's planned and operating reactors into five categories of population density in order to decide which to recommend for special risk studies.

New York's Indian Point site, 30 miles from Manhattan, is at the top of the NRC's list of sites with "substantially above average" population levels nearby, but is closely followed by the Limerick plant outside Philadelphia and the two reactors at Zion, Northwest of Chicago.

Ranked "above average" in population were the sites at Bailey, near Gary, Ind.; Beaver Valley near Pittsburgh; Fermi near Detroit; Millstone, near New London, Conn.; Seabrook in New Hampshire; Shoreham in New York; Three Mile Island at Middletown, Pa.; and Waterford, near New Orleans.

Victor Stello, the NRC's chief of inspection and enforcement, said he was sending New York state and county officials a list of problems in their emergency plans, ordering that they be corrected within 120 days. He said the Federal Emergency Management Administration had found that state and county governments were either uncertain or quarrelsome over which had authority to order emergency plans into effect and which parts each would carry out.

At an April 15 meeting of government officials, utility executives and the NRC, county officials complained they had no authority to direct the police, fire or recuse teams of the cities and townships in their areas, Stello said. The various executives also disagreed on who should pay for any emergency action and on who should collect and handle the funds.

"They say they need legislation to straighten it out," Stello said in an interview. He added that cooperative agreements could serve the same purposes and avoid any NRC disciplinary action, which legally could include a plant shutdown. That is not likely, however, since the NRC is trying to prod the governments and not the utilities.

The reactors involved are the two at Indian Point near New York City, the Ginna plant at Scriba, and the Nine Mile point and Fitzpatrick plants near Oswego.