Many New Yorkers who approached the first morning of their bus and subway strike today were grinning warily by midday as pleasant weather and a large number of stay-at-homes turned an expected disaster into an easy commute or an enjoyable holiday.

For one day, at least, New York dodged the bullet.

"Things are going well," Mayor Edward Koch said of the elaborate contingency plan suddenly thrown into effect but never expected to be totally successful in the absence of a transit system that carries 6 million riders daily.

"The strnge thing is that it's working," he added.

With a bright sun and 50-degree weather to cheer them on their way, New Yorkers by the thousands walked, roller-skated, bicyled, car pooled and boated to work.

Some flew.

Stanley Safery and three other Wall Street executives rented a helicopter to fly them from a suburban Westchester County airport to the heliport in Wall Street.

The trip took 15 minutes and cost each rider about $80 round trip, Safery said. "It's cheaper than a hotel room. The bottom line is I wish I was rich enough to do it every day," said Safery, vice president and manager of executive and corporate services for the brokerage house Drexel Burnham Lambert Inc.

New York's first systemwide transit strike since 1966 began at 2:05 a.m., when the 33,600-member Transport Workers Union voted to strike the debt-ridden Metropolitan Transportation Authority. Four hours later, seven unions struck the nation's largest commuter railroad, the Long Island Rail Road, which carries 200,000 riders a day.

Even as they marveled at the ease with which the city coped today, Koch and other officials pointed out that the first day of the 1966 strike was the best.

Before this strike is over, the union leadership is likely to be imprisoned, businesses will have lost an estimated $150 million daily, wage earners, missed thousands of paychecks and the camaraderie of a first day of adventure probably turned to joyless routine, at least for those without helicopters.

The Passover holiday, spring vacation at many schools and the apparent willingness -- if not eagerness -- of many to take at least one day off from work, kept the crowds down. On the first day of the 1966 strike, office absenteeism was close to 40 percent. By the end of the 12-day strike, it was about 10 percent daily.

"We had a lot of conversions," deputy transporation commissioner Sam Schwartz joked about the Jewish holiday. "Thursday is Holy Thursday, so I bet a lot of people will revert back to being Christian."

For some workers, the strike will become a long-running house party. American Express has converted two floors of its 40-story headquarters into dormitories for workers in its travelers check department. One floor is for women, one for men. Free breakfast will be served daily and dinner and snacks will be available in the company's cafeteria.

In the bar of the Drake Hotel, a giddy crowd unused to finding themselves in a hotel together at their several employers' expense was enjoying Monday night, even as the negotiators struggled through the final hours of their efforts to avert a strike.

"Queens is staying in New York," a Manhattanite not used to such crowding remarked with disdain.

Hotel rooms are impossible to find, and some were being occupied by squatters refusing to abandon rooms reserved by others. At one Holiday Inn harried managers tried to threaten and cajole guests to leave, while those with reservations ended up sleeping several to a room on camp beds. w

While many key employes are in rooms booked long in advance by prudent companies, others were ferried to work in company buses.

The New York Stock Exchange, Merrill Lynch, Pierce, Fenner and Smith and Columbia University were among those chartering buses to pick up workers at designated sites.

American Express rented cars as well as buses, and now boasts a 100-foot excursion boat that can carry 250 people at a time across the East River to Pier 9 in lower Manhattan.

Already the strike has given birth to a new uniform for the working man -- a three-piece suit and running shoes. One after another, pairs of feet shod in red, yellow, blue and orange strolled where oxfords and wingtips usually are found.

Koch said that 25,000 people bicycled to work, and long lines at bike stores of people seeking repairs for machines just retrieved from basements indicated that the number will grow. About 30,000 walked into Manhattan, Koch said.

The mayor, a strong advocate of a tough bargaining stand against the Transport Workers because he must negotiate with the city unions this summer and does not want to be under pressure to match any large transit settlement, met walkers and bikers on the Brooklyn Bridge during the morning rush hour to urge them on.

"The problem is that everyone cooperates on the first day. The question is will you have the same spirit if the strike goes on, as it may very well, for a few days," he said. The TV cameras and reporters accompanying the mayor blocked half the bridge's pedestrian lanes, to the annoyance of some commuters.

Even businesses heavily dependent on people who ride buses and subways were doing well. A U.S. Postal Service aide, Mildred Lee, said 7o percent of the workers at carrier stations were present by 10 a.m. and 60 percent were on hand in the terminals.

"The one difference is that in 1966 nobody believed there would be a strike. This time we are prepared," she said.

The strike began after the transit authority apparently misjudged its timing in the last-minute negotiations. With militant union leaders demanding pay increases of 12 percent a year for two years for their $8.08-to $8.90-an-hour rank-and-file, the authority waited until less than an hour before the midnight strike deadline to raise its offer to 6 percent in each of two years.

The authority knew the offer would be rejected, but hoped for a counter offer from the union close to its secret top figure -- believed to be 8 percent a year.

"It was all too late. It was much too late," said John O'Donnell, counsel to the union. "Tempers were aroused by that time."'

Chief mediator Walter Gellhorn won two hours more from the union leaders and outlined for them and for key management people an 8 percent solution. The union rejected it without detailed consideration.

New York law makes strikes by public employes illegal, and imposes mandatory fines of two days' pay for each day a worker stays out. Jail terms can be given to union leaders. The union treasury stands to lose the roughly $100,000 a week in dues checkoffs paid to it by management.

Union leader John Lawe has said a strike may destroy his union and bring great hardship to individual members.

Even in running shoes, New Yorkers are unlikely to dodge the discomforts of traffic jams and the pain of business losses for very long. And when the subways and buses start running again everyone knows that they will cost more, perhaps as much as 75 cents instead of the 50-cent ride that was available until early this morning.