September 11, 1986

FOR the owner of the small bathroom - that irksome five-by-seven-foot space devoured by tub, sink and toilet - mornings can be mean. Ordinarily serene couples wrangle over mirror time. Body movements are choreographed to avoid slips and collisions, while cotton balls tumble from packed medicine cabinets. It doesn't have to be that way. Architects and designers can manipulate the elements - from mirrors, lights and fixture sizes to color schemes and ceiling heights - to give even a sliver of a bathroom a feeling of expanse and elegance. ''Basically, it's an issue of creating the illusion of space,'' said Nate McBride, a New York architect. Most American bathrooms fall into the ''small'' category. According to the National Kitchen and Bath Association, 80 percent of all bathrooms in the United States are under 60 square feet, the cutoff for what is considered small. But even in homes with bathrooms the size of living rooms - tropical sanctums combining fine art, exercise and glamour - there can be others the size of closets.

Mayor Koch said yesterday that Senator Alfonse M. D'Amato had been ''a superb Senator,'' a better lawmmaker than his newly chosen Democratic opponent, Mark Green, would be. ''I don't happen to agree with Mark Green's philosophy so I am never going to endorse him,'' the Mayor said at a City Hall news conference a day after Mr. Green defeated John S. Dyson in the Democratic primary. Asked if Senator D'Amato, a Republican, was a better Senator than Mr. Green would be, the Mayor responded, ''No question about it in my mind.'' The Mayor, who had supported Mr. Dyson in the primary, declined to say whether he would endorse anyone in the general election. Mr. Dyson will be on the ballot, on the Liberal line. Role of Ideology In an election year in which political analysts said ideology was generally de-emphasized in the primaries around the country, both Senator D'Amato and Mr. Green, in separate news conferences, indicated its importance in New York. They tried to paint each other into political corners, with Senator D'Amato charging that Mr. Green was a candidate of ''left-wing ideologues'' and Mr. Green responding that the Senator was ''a right-winger.''

A manufacturer of electronic taxicab meters suggested to the City Investigation Department in 1982 that there was corruption at the Taxi and Limousine Commission. But the contractor's attorney, State Senator Emanuel R. Gold, Democrat of Queens, said that after sending a letter to the Investigation Department with the suggestions of corruption, ''I never heard from them again.'' In the letter, Mr. Gold said he and his client believed that the department was not competent to follow up the allegations and that he was prepared to take them elsewhere. Mr. Gold disclosed the letter yesterday, a day after the United States Attorney in Manhattan in the early 80's, John S. Martin Jr., issued a report saying that the Investigation Department received repeated indications in 1982 and 1983 of corruption at the Parking Violations Bureau, but botched the investigations.

Israelis Strike in Lebanon Israeli planes struck at suspected Palestinian bases in southern Lebanon after Israel foiled an infiltration attempt by guerrillas.

When the Nissan Motor Company recently wanted to expand its Mexican subsidiary, it took a most unusual route. First, Nissan went into the financial markets and bought $60 million in Mexican Government debt. Because Mexico is in financial trouble, Nissan paid only $40 million for the debt. It then resold the debt to the Mexican central bank for $54 million in pesos - which it then promptly invested in the Mexican subsidiary. The result: Some $60 million in Mexican Government debt was wiped out; Nissan had more equity in its Mexican operation, and Citicorp, Nissan's investment banker, pocketed a fat fee.