Political advertisements often have a dreary sameness to them, so in the New Jersey gubernatorial primary -- which includes a record 21 candidates -- many people have taken note of the television spot that features the endorsement by the talking dog.

The dog -- who supports Jersey City Mayor Thomas F.X. Smith -- is not the most attractive canine to grace the TV screen; it's merely a mutt who jogs with the mayor along the waterfront. What the dog has to say seems not that original, either: ". . .In my opinion New Jersey needs a guy like Tommy Smith. See you in Trenton, Aaaaaarf!"

Still, as Dr. Johnson might have said, the remarkable thing should not be that the dog endorses his candidate badly, but that he endorses him at all. That he endorses him at all is, of course a serious political decision.

"with 23 -- oh, you're right, 21 -- candidates in the race, most of whom had produced and are airing TV commercials all against crime and toxic waste and all in favor of motherhood, the voters very rapidly stop paying attention," says Smith's campaign manager, Bob Janiszewski. "you need something unusual."

With 13 Democrats and eight Republicans on the ballot, the June 2 gubernatorial primary is a media consultantS nightmare. The polls, even at this late date, show the voters 50 percent undecided, and many campaign managers agree that most Jersey voters probably could not list even half the candidates' names.

"maybe they could name three or four," says Karl Struble, president of National Voter Contact Inc., which is handling the campaign of Democrat Joseph P. Merlino.

The size of the field -- which does not include the 11 independents and small-party candidates who will be on the general ballot in November -- has been ascribed to many things. There is the fact that the incumbent, Democrat Brendan Byrne, by state law cannot run for another term; the fact that New Jersey -- with no statewide elected offices other than governor -- traditionally stages a large governor's race, ambitious politicians having few places to go.

But the main reason for the number of candidates probably is the state's controversial public financing law, which for the first time this year includes the primary, and which so far has contributed over $5 million to the candidates. That includes a payment of $258,000 to a candidate who four weeks before the primary dropped out.

The most generous public financing law in the country and the only one-that covers gubernatorial primiaries, New Jersey's is called "the politicians' full employment act." It gives any politician who has raised $50,000 in contributions of $800 or less two dollars for every additional dollar raised, with a ceiling of $600,000.

"only one candidate has, as we say, hit Bingo," says William Schmidt, assistant executive director of the New Jersey Election Law Enforcement Commission. Four more, however, are very close.

The bill could also be called the New York and Philadelphia television enrichment act and the ambitious politician's steppingstone act. Since Jersey lacks homegrown television stations, most of this Jersey taxpayers' money will be spent out of state. And, some of the candidates appear to have little interest in being governor but are taking advantage of the public financing to run state-wide and get name identification prior to running for Harrison Williams' Senate seat next year.

Originally the brainchild of Gov. Byrne -- who this year tried to amend the law by raising the qualifying figure from $50,000 to $150,000 -- the public financing law has now become a issue in a somewhat issueless campaign.

A number of Democrats who insist that the bill was right in principle concede that it at least must be amended ("A worthy experiment, but it has to be changed," says state Democratic executive director Pete Curtin). The Republicans are seizing on it happily as an example of Democratic mismanagement.

"from my personal standpoint, the person who created it should have been taken out and shot," says Republican executive director Dave Ehrling.

"it's confused the whole selection process. I seriously wonder how many in this late game would still be in, if not for it . . . . They've removed the normal obstacles that any candidate who was running for office would have to face. . ."

"when you get an issueless campaign, and the voters are bombarded with 13 Democrats and eight Republicans, the voter is going to get confused," he says."and when it's this late and 50 percent are still undecided, that tells me they're not going to vote -- that's the worse thing, they're not going to vote."

Only one of the candidates who could qualify for public funding has refused it; Bob Roe, a Democratic congressman from Passaic County who is a front-runner and who finished second to Byrne in the 1977 primary, has made public funding an issue (Bob Roe for Governor Committee, which has raised this money without resorting to the use of taxpayer money in this partisan campaign").

Roe has so far raised $600,000 and, as part of his strategy, has avoided large political forums -- including a local talk show in which 18 of New Jersey's gubernatorial candidates crowded into a studio.

"we call them beauty contests or meat markets," says campaign manager Dan Horgan. He calls the public finance law "bizarre," and holds it responsible for the "massive invasion" of gubernatorial contenders. "the state projects a $100 million shortfall between revenue and spending, and they'll probably spend $10 million for politicians to put their commericals on television," he says.

Another candidate who has refused public funding is Essex County finance chairman Joseph A. Sullivan, who is also making it an issue. Having spent $1 million of his own on the campaign, Sullivan would be precluded from accepting state funds, according to the Election Law Enforcement Committee. However, Sullivan's media consultant, Alex Ray of the Chesapeake Media Management Group, says that Sullivan made a decision not to accept public funding very early in the campaign.

A candidate who will spend $7000,000 on television ads, Sullivan is a front-runner in the Republican State Committee -- Thomas H. Kean, a former speaker of the assembly (he was endorsed by Gerald Ford), and Lawrence F. Kramer, the mayor of Paterson.

On the Democratic side, in addition to Congressman Roe, Congressman James J Florio, who finished fourth in the '77 primary, is reportedly a strong candidate, as are Joseph P. Merlino, the president of the State Senate, and John J. Degnan, Byrnes's attorney general, whose campaign is being handled by New York hotshot consultant Dave Garth and is seen -- though there has been no formal endorsement -- as Byrne's man.

Other strong contenders are Smith -- of the talking dog endorsement -- and Newark Mayor Ken Gibson, the only black in the race.

Most recent polls, however, indicate that none of the candidates, Democrat or Republican, has more than 15 percent of the vote, and at least eight are between 7 and 15 percent.

It's a figure -- and a race -- that seems to give the TV commercial of Joseph Merlino a special meaning.

The ad features Merlino and a card, much like an American Express card.

"you probably don't know me . . ," Merlino says.

In Jersey this spring, he's probably right.