I was with Robert F. Kennedy in California just before his assassination. Forty years after his death on June 6, 1968, it is still difficult to think about what might have been.

As each anniversary passes, the pain returns. RFK's haunting, handsome face touches us from the cover of this month's Vanity Fair.

Each year, the nation mourns anew.

The grim news of Sen. Edward M. Kennedy's recent diagnosis and operation is tempered with the solace that his sunset will not come at midday.

Today, very personal memories always surface.

Christmas Eve 1963, only one month after burying John F. Kennedy, Bobby attended my father's funeral. He delivered a note to my mother from Jacqueline Kennedy: "I don't think Jack would have been president without Billy Green," she wrote. "Maybe they will find each other - I hope so - though it isn't exactly the way I picture heaven."

What generosity, after all he had been through, with all his children waiting at home.

Two weeks later, Bobby phoned me. He knew I wanted to run for my father's seat in Congress but faced resistance from Mayor James Tate and other party leaders. I was 25 and still in law school. "Run," he said. "You will win, and we will help."

All doubt was gone. I was running, with or without the party endorsement. At Bobby's urging, I visited him in Washington in January 1964, and I thanked him. "Don't you know what your father did for my brother," he said, his head down. I'd never seen a sadder face in all my life. I haven't yet.

Bobby and I had met before in happier times. First during the 1960 campaign and during the 1,000 days of Camelot. One of my fondest memories is the day my father called and invited me to Washington. Bobby was taking us on a Potomac cruise on the Honey Fitz, the yacht JFK named after his grandfather.

I had always hoped and expected that Bobby would run for president. So when he did I was aboard.

I was party chairman in Philadelphia, but in truth at Mayor Tate's sufferance. I supported RFK and Tate was furious.

I had arranged for him to be the speaker at the Philadelphia Democratic Party's annual fund-raising dinner in April 1968. But after RFK announced his candidacy, Tate demanded I withdraw the invitation.

I refused. I planned a midday rally at 15th and Chestnut Streets for the day of the dinner. People were packed in like sardines, from 19th to 13th Streets and from Market to Walnut. Eight thousand attended the dinner, a record never again approached.

President Lyndon B. Johnson decided not to seek reelection. Bobby started winning primaries. Tate and other state party leaders herded the Pennsylvania delegates to Harrisburg and forced them to declare for Vice President Hubert H. Humphrey. A handful of us voted for Kennedy. I held a news conference labeling their rump meeting a "Pennsylvania Railroad" and vowed we would meet again after California.

In the days leading up to the California primary, I campaigned up and down the Golden State for RFK. On June 4, we met in his suite at the Fairmont Hotel in San Francisco and discussed how to win over the Pennsylvania delegates. Victory was in the air, but I had work to do for RFK back in Philadelphia.

So I left California on primary day morning. I arrived home, watched the returns, listened to his victory speech, turned off the TV and went to bed euphoric.

I got a call in the middle of the night from a reporter who told me the awful news. I couldn't speak. . . . I cried and prayed.

What would have been, no one can say. No Nixon? No Watergate? Less trauma in Vietnam? No one knows.

But I do know this: From his pain he emerged a wiser and even more compassionate man.

As president, he would admit his mistakes. War would be the very last resort. We would talk to our advisers and listen. Containing nuclear weapons would be an urgent focus. He would be welcomed around the world.

He would fight the corrupt, and challenge the greedy and the comfortable. Most of all, he would remember the forgotten - those stuck in urban ghettos, mostly black; those in rural hallows across the land, mostly white; and those picking our crops, mostly Hispanic. Better yet, they would know it. They would see it in his face.

That is what might have been.

Robert F. Kennedy said: "We can do better." He was right.

Bill Green was a U.S. congressman from 1964 to 1977 and mayor of Philadelphia from 1980 to 1984.