In all the talk of the presidential race, little attention has been paid to contests for the U.S. Senate. Depending upon how the political winds blow, November could bring either a debacle for the Republicans, or in their best scenario, a 50-50 split.

Only if everything goes just right for the GOP could the party regain the control it lost two years ago. The math is not encouraging.Fifteen Republican and 18 Democratic seats are at stake. Democrats are as certain as certain can be to hold 10 of them: Texas, West Virginia, Arizona, Massachusetts, Hawaii, Maine, New York, Michigan, Maryland and Tennessee.

The Republicans, by contrast, have only six sure bets: They will re-elect Hatch in Utah, Lugar in Indiana, Danforth in Missouri, Roth in Delaware, Heinz in Pennsylvania and Wallop in Wyoming.

Almost everything else is up for grabs. Nine Senate seats now held by Republicans are in differing degrees of jeopardy. Eight seats held by Democrats are at risk. This is how local editors and Washington observers see the prospects:

On the Republican side: One GOP seat is lost before the campaign begins. Virginia's former Democratic Gov. Charles Robb will win the seat abandoned by Republican Paul Trible. This will be a landslide. In Nevada, Republican Chic Hecht will have to come from behind to defeat popular Gov. Richard Bryan. He probably won't make it.

In Rhode Island, a normally Democratic state, John Chafee will be hard put to retain his seat against Lt. Gov. Richard Licht. In Minnesota, Dave Durenberger will have to overcome a coattail vote for presidential candidate Michael Dukakis in order to defeat Humbert Humphrey III. In Nebraska, Republican David Karnes will need all the boost he can get from presidential candidate George Bush in order to get past former Gov. Bob Kerrey.

In California, Pete Wilson looks in good shape now, but his race against Lt. Gov. Leo McCarthy is tightening. In Connecticut, Lowell Weicker probably will survive, more's the pity.

Republican seats are vacant in Washington and Vermont as well as in Virginia. In Washington, former Republican Sen. Slade Gorton could make a comeback by defeating either Rep. Don Bonker or Rep. Mike Lowry. In Vermont, Rep. Jim Jeffords is a good bet to retain the seat held by retiring Sen. Robert Stafford.

Democrats probably can hold New Mexico and Montana. Six other seats held by Democrats offer a prayer for the GOP. In three states, incumbents have fights on their hands. In North Dakota, 80-year-old Quentin Burdick, now recovering from a serious illness, faces an aggressive campaign by Earl Strinden of Grand Forks. In New Jersey, Frank Lautenberg is getting unexpectedly tough opposition from Republican Pete Dawkins. In Ohio, Howard Metzenbaum is running into more trouble than he expected from Cleveland's Republican Mayor George Voinovich.

The other three Democratic seats are open, owing to the retirement of Lawton Chiles in Florida, John Stennis in Mississippi and William Proxmire in Wisconsin.

Republicans may have the best chance of picking up a victory in Florida. Their candidate, popular Rep. Connie Mack, will have a reasonably united party behind him.

Mississippi can look forward to an exciting race between Republican Rep. Trent Lott and Democratic Rep. Wayne Dowdy. The candidates offer a clear choice between the conservative Lott, who will do well in the southern part of the state, and the liberal Dowdy, who will take virtually all of the state's heavy black vote. Much will depend upon the black turnout.

If Republicans could offset losses in Virginia and Nevada with gains in Florida and Mississippi, they would need to hold the remaining 13 Republican seats just to retain the present division of 54-46. To regain a majority would require victories in Wisconsin, Ohio, New Jersey, North Dakota and Montana. It's uphill all the way.