Ted Kennedy is back in business.

Two years ago this week, Kennedy watched President Carter's forces use a wave of highly personal negative ads to force a standoff in the Pennsylvania primary that sealed the failure of Kennedy's bid for the Democratic presidential nomination.

One year ago, he watched from a seat on the floor of the House as President Reagan, in a masterful address to a joint session of Congress, launched the drive for passage of a budget and tax program diametrically opposite to the policies Kennedy had pushed for almost 20 years in public office.

Sen. Edward M. Kennedy (D-Mass.) appeared to many--including some of his own supporters--as a politician whose time had come and gone.

But this morning, when Kennedy delivers the opening address to the American Newspaper Publishers Association convention in San Francisco, he looks like anything but a has-been.

He is riding the hottest new issue in American politics--the nuclear arms freeze. It is an issue he grabbed from other eager Democrats, some with much longer identification with arms control, in a display of fast footwork that caused some heads to spin.

His early and sometimes strident opposition to Reaganomics, which made him odd man out in 1981, is attracting a lot more company in recession-ridden 1982.

His recent television appearances have shown signs that he has cured the verbal stumbling that marred his famous Roger Mudd interview in 1979 and many of the early speeches of his inept 1980 campaign.

There has been a series of magazine features, emphasizing his closeness to his children--and not the separation from his wife, the reports of womanizing and the echoes of Chappaquiddick that accompanied him in 1980.

And the early polls--for whatever they are worth--show him running about 3 to 2 ahead of his best-known potential rival for the 1984 nomination, former vice president Walter F. Mondale.

All this has made Kennedy a hot political property--much in demand. While concentrating his time and effort on his reelection campaign in Massachusetts, he is doing the kind of chores that keep him visible and politically viable.

The California weekend trip that was built around this morning's speech to the publishers, for example, also included a meeting with the Los Angeles Times editorial board, talks to the Los Angeles County Democratic executive committee, a Hispanic labor group, and a group of West Coast supporters of Brandeis University, appearances at fund-raisers for two key California Democratic congressmen and a series of television interviews.

In the last four months, he has managed to squeeze in similar trips to New York, Illinois, Ohio, Pennsylvania, Wisconsin, Florida, Georgia, South Carolina and Rhode Island.

The first test of Kennedy's comeback will be his Massachusetts Senate race, for which he had raised more than $1.7 million by the end of last month. His novice Republican opponent, businessman Ray Shamie, released polling data 10 days ago that purport to show Kennedy losing favor at home. According to the Decision Making Information Inc. poll in late March, Kennedy's approval rating was down 4 percentage points from last September to 61 percent, and his disapproval rating was up 8 points to 34 percent. Kennedy's lead in a trial heat against Shamie had dropped from 63 to 11 to a still healthy 53 to 22.

An independent poll for the Boston Herald-American, covering comparable periods, showed a 5-point jump in Kennedy's negative rating and a 32-point lead over Shamie, who is still fighting for name recognition with most Bay State voters.

Most politicians have long assumed a Kennedy victory in Massachusetts, and will measure his performance against his previous vote totals of 55, 74, 62 and 69 percent in 1962, 1964, 1970 and 1976.

In the political community, his dexterity in grabbing the arms-freeze issue is taken as evidence that Kennedy cannot be discounted. The senator had a long history of interest in the issue, and had sat in on earlier arms-control talks in Geneva. But he has never served on the Foreign Relations or Armed Services committees, and his stock in trade has been domestic issues, not foreign policy.

Aides say Kennedy was alerted to the issue back home in Massachusetts and started intensive briefings last winter. Even though such potential presidential rivals as Mondale and Sen. Alan Cranston (D-Calif.) endorsed the freeze movement earlier than Kennedy did, it is the resolution that Kennedy co-sponsored with Sen. Mark O. Hatfield (R-Ore.) that has become its focus.

Staff members rushed out a mass-market paperback on the dangers of atomic warfare under the names of Kennedy and Hatfield. And Kennedy now talks nuclear freeze--not his old standbys of national health insurance, tax reform or energy price controls--in most major speeches and in the heavy run of television and press interviews that dot his schedule in Washington and on the road.

A corollary benefit of his move back into the spotlight is that it has given Kennedy a chance to show off his more controlled and polished speaking style. There are few of the "uhs" and "aahs," the long pauses or the broken sentences that dotted his disastrous interview with Mudd on the eve of his 1980 race and that led to pressroom caricatures of his campaign speaking style.

Aides deny the rumors that Kennedy has been coached by his new media adviser, Michael Kaye, but they concede that when the senator got around to looking at news clips of himself on television, after the 1980 campaign, he did not like what he saw.

The booming voice and big gestures he used for rally speeches seemed exaggerated and harsh on the small screen, and the contrast with his stumbling interviews added another distracting element to the picture. Quite deliberately, Kennedy has adopted a calmer speaking style--and with it has come a greater flow and continuity to his words.

How well the new style works will probably be given its most important test at the Democratic Party mid-term conference in Philadelphia in June. Kennedy, Mondale and other presidential hopefuls are expected to make speeches during the weekend.

In Kennedy's case, he will be measured not only against his rivals but against the memories of the oratorical triumphs he scored, in his old, full-throated style, when he addressed the mini-convention in Memphis in 1978 and the Madison Square Garden convention after his withdrawal of candidacy in 1980.

For now, the polls are looking very comfortable. A Gallup Poll of Democratic voters in January put Kennedy ahead of Mondale, 54 to 31. A Harris poll of Democrats and independents in March gave Kennedy 32, Mondale 20 and Sen. John Glenn (D-Ohio) 13 percent, with others trailing.

A Mondale aide noted that Kennedy had enjoyed even larger leads over Carter before declaring his candidacy in 1979. Despite Mondale's heavy travel schedule this year and from 1976 through 1980, the aide noted, the former vice president never has run a presidential campaign, as Kennedy did. "I'd be more worried if the polls looked like this at the end of 1983," this aide asserted.

But Peter D. Hart, who polled for Mondale in Minnesota Senate campaigns and for Kennedy in the 1980 presidential race, said he thought the current polls are far more significant than those that showed Kennedy leading Carter in 1979.

Kennedy "has gone through the firestorm of a national campaign, and people know all the things that were said about him," Hart remarked. "They've sorted them through and they're still willing to say they are for him. That doesn't mean they are giving him the nomination, but they are certainly ready to listen to what he has to say."

And Ted Kennedy is out there--talking.