A 13-member Chinese navy delegation is in Washington for more than a month's discussions on how the U.S. Navy might assist China in modernizing its surface fleet.

Pentagon spokesman Michael I. Burch would not specify what the Chinese were interested in obtaining from the United States. But industry sources said the Chinese have stressed their desire for American anti-ship missiles and turbine engines to build a navy with punch and speed without the expense of building aircraft carriers and cruisers. The Chinese also hope to build a new generation of destroyers.

"They are after a coastal defense navy, just as Russia was before she went blue-water with big ships," said an industry executive whose firm is among those trying to win contracts to modernize the Chinese navy.

China's present navy features 100 diesel-powered submarines for coastal defense along with 14 old destroyers, 22 frigates and eight patrol boats. Navy Secretary John F. Lehman Jr. went to China in August and discussed the possibility of destroyers exchanging port visits. Burch said such arrangements have not been made.

Asked why the Pentagon helps build up the defense capability of the communist government of China at the same time the Reagan administration is deploring the Marxist military threat posed by Nicaragua, Burch replied: "In the last several years we have found that the Chinese are interested in promoting stability in that area of the world. To date there have been no arms sales. You might also note that we have sold weapons or have considered weapons sales to such countries as Yugoslavia."

On another subject, the administration's concern about Soviet MiG21 fighter planes going to Nicaragua, Burch said "it is sometimes a fine line between whether a weapon of any type is purely defensive or offensive." He said the MiG21s, which the Pentagon has considered a home defense weapon for the Soviet Union, "would have a destabilizing effect on the balance in the region" if introduced in Nicarauga.

Asked if MiG21s in Nicaragua could be considered a defense against Honduran aircraft, which include 10 A37 Dragon Flies light bombers and 12 Super Mystere fighters, Burch said that is a judgment call based on a combination of factors, including the doctrine of the country's leaders. Honduras for more than a year has been seeking to upgrade its air force with F5 fighter jets from the United States.