If ever there were a city that needed a good subway system, it is New Delhi, India, one of the world’s most populous (14 million) and most crowded metropolises. Now the city’s got just that, and everyone, from residents to foreigners, is amazed and thrilled by its success. Although the entire 62-mile, 90-station subway system won’t be complete until the end of the decade, the first part opened on time and on budget — a cause for celebration for any public-works project, and a rare occurrence in India. The project, which was begun four and a half years ago and opened last month, is being hailed as a political, managerial, and engineering triumph. Hundreds of thousands of people are using the subway already, from curious tourists to eager children to commuters in outlying communities.