Sixteen candidates are running for the Senate in Tuesday's Pennsylvania primary. But most politicians believe there are really no contests at all.

That's because in both the Republican and Democratic primaries, one well-known candidate is running against seven poorly-financed and little-known opponents.

The front-runners for the seat being vacated by retiring Sen. Richard Schweiker (R-Pa.) are Democrats Pete Flaherty, the former mayor of Pittsburgh, and Republican Arlene Specter, a former Philadelphia district attorney. However, both have reputations as losers and a race between them in the fall does not excite professional politicians.

Flaherty made his name as a maverick mayor who cut taxes and fired city workers. He alienated most elements of the Democratic Party -- including unions, blacks and liberals -- but became a hero of snorts with blue-collar voters.

He was defeated by Schweiker in 1974 and, after serving a year as deputy U.S. attorney general in the Carter administration, lost a gubernatorial race to Richard Thornburgh in 1978.

His major opponents this year are Temple University law dean Peter Liacouras, former Iowa representative Ed Mezvinsky and state Rep. Joseph Rhodes Jr. of Pittsburgh.

Rhodes, who is black, was thought to have the best shot at beating Flaherty, but his chances were hurt when former commonwealth secretary C. Delores Tucker, a popular black politician in Philadelphia, entered the race.

Republican Specter, once the boy wonder of Philadelphia politics, is also trying to break a losing streak, He was defeated for reelection as district attorney in 1973, lost to Sen. John Heinz in the 1976 GOP primary and lost to Thornburgh in the 1978 primary.

His major opponents are former GOP state Chairman Harold (Bud) Haabestad and state Sen. Ed Howard of Bucks County outside Phildelphia.

Haabestad got into the race at the urgings of Thornburgh, Heinz and Schweiker.

But many professional Republicans are angry at Thornburgh and Haabestad for freezing them out of patronage jobs and this -- plus the fact that Haabestad is still largely unknown -- has made Specter the strong favorite.