More than 1,200 local seniors who came by bus from rest homes across Cambridge were treated to more than just lunch yesterday in Harvard Yard. They also saw a dancing University president, their mayor in a sailor's cap and even a life-sized mermaid.

President Neil L. Rudenstine, Mayor Kenneth E. Reeves '72 and more than a dozen other city officials and candidates were on hand to greet the seniors at the 20th annual Harvard Yard Picnic.

The event, a goodwill gesture on behalf of the University, is one of the premiere collaborative efforts between a city and school who often find much to disagree about.

The seniors found the day most agreeable. They enjoyed a lunch of chicken and rice, sang along with the Union Orchestra and watched the Roxy Dancers perform classical dances of Indian and South American origin.

Rudenstine, appearing vibrant after a month in Europe, seemed to enjoy himself during his hour at the picnic.

He mingled freely with the senior citizens, stopping to chat at several tables. ("He looks like he's running for city council," joked Councillor Michael A. Sullivan)

In keeping with the spirit of the day's "Ship Ahoy Cambridge" theme, Reeves dubbed Rudenstine the "captain of the good ship Harvard" and presented the president with a sailor's cap.

And in his remarks to the seniors, Rudenstine related a legend about an English gentleman who had no sailing experience but became an admiral in the British navy because he was "always at sea."

"Similarly, the only reason we have this picnic is because we have always been at sea," Rudenstine joked of Harvard.

Rudenstine said he enjoyed the opportunity to meet the Cam- bridge citizens.

"This is one of the days where Harvard andCambridge celebrate the fact that they are ourneighbors and take time to enjoy each other'scompany," he said.

The seniors appeared to have fun as well,despite the heat and humidity.

"I think it's great." said Eileen McGaughey, aretired secretary. "It's a great band, good food,and that's the first time I've ever seen thepresident of Harvard."

Another senior said he enjoyed the picnic as areunion of sorts.

"I get to see people I worked with 30 yearsago," said Charles C. Smith, a retiredsalesperson. "It's very good and very nice."

City officials agreed that the day was asuccess.