Despite Democrats' optimism that Michael Dukakis is on the road to the White House, the obstacles presented by the Electoral College make it a difficult and uncertain path.

Although polls show the Democrats have reason to be optimistic, U.S. elections are not decided by public opinion polls or by popular votes. They're decided in the Electoral College, and that makes it tough for the Democrats.The college is fed by 50 separate winner-take-all state elections plus the District of Columbia voting, and it is "nothing less than an electoral Matterhorn" for Democrats, says Democratic consultant Pat Caddell.

There are two basic reasons for the Republican advantage:

- In the makeup of the Electoral College, each state gets as many votes as it has representatives and senators. That produces what senior Dukakis adviser Dick Moe calls the "small-state bias." This works to Bush's advantage, because, Moe says, Bush "has an enormous edge in smaller states that are overrepresented in the Electoral College."

In the past five presidential elections, Republicans have won 53 percent of the popular vote but 77 percent of the electoral votes.

- Bush has a much larger base of seemingly solid support from which to work, based on voting patterns in the last five presidential elections. In those contests, of which the GOP won four, only the District of Columbia, with three electoral votes, voted Democratic every time. Yet 23 states with a total of 202 electoral votes - 68 short of the 270 needed to win the White House - voted Republican every time.

Put another way, since 1952, the Republicans have averaged 55 percent of the vote in 27 states with 208 electoral votes. That is a formidable base.

Dukakis says Democrats "will contest every state." He'd be expected to say that. An examination of the politics of the various states, their history and current polling data provides a more realistic scenario.

The election likely will turn on three groups of "swing voters" who have voted Republican heavily in the past decade:

- White ethnics in key northern states.

- Young suburbanites, most of them "baby boomers."

- Southern white men.

There are some states in which few political analysts expect Dukakis to make a really serious effort: New Hampshire, Colorado, Oklahoma, Arizona, Utah, Nevada, Idaho, Montana, Wyoming, North and South Dakota, Nebraska, Kansas and Alaska. Count these states - with their 68 electoral votes - in the Republican column.

Dukakis says he'll fight hard for another 90 electoral votes in the South - Florida, Alabama, Mississippi, Tennessee, South and North Carolina, Kentucky and Virginia. It'll be an uphill fight; they figure to go Republican.

Massachusetts, New York, Rhode Island and the District of Columbia - with a total of 56 electoral votes - appear to be safely in Dukakis' column.

That leaves the remaining 25 states - and 355 electoral votes - potentially winnable by either side in a close election. Bush figures to need only 107 of them, while Dukakis would need 214.

Of those states, Indiana, Arkansas, Louisiana, New Mexico and Georgia - with 45 electoral votes - seem to be leaning toward the Republicans.

Meanwhile, Pennsylvania, West Virginia, Maryland, Connecticut, Hawaii, Iowa, Minnesota and Wisconsin, with a total of 82 electoral votes, lean toward the Democrats.

Of the remaining 12 states - vote-rich California and Texas, major "frost belt" centers of Illinois, New Jersey, Ohio, Missouri and Michigan are the battlegrounds where the candidates' time and money will be concentrated. These represent 170 electoral votes. (The other five closely contested states - Maine, Vermont, Delaware, Oregon and Washington - have only 27 electoral votes among them.)

Dukakis has to win most of this crucial group of seven big states in order to move into the White House. Losing as few as three (under some scenarios only two), or just California by itself, will probably mean defeat.

Here's a look at the key battlegrounds:

No. 1 is California, with 47 votes, the largest single prize. "If the Democrats don't win California, I don't see how they can get 270 electoral votes," said Democratic pollster Peter Hart.

Although polls show Dukakis ahead there, the state hasn't gone Democratic since 1964, and it's a safe bet that President Reagan - still popular there - will spend a great deal of time in his home state stumping for Bush.

The races in Illinois, Ohio, Missouri and Michigan generally boil down to Democratic urban areas vs. Republican rural and small towns. The suburbs will decide the winner. The GOP has prospered in recent years by winning the mostly white suburban vote, but Dukakis has shown some appeal to it.