BOSTON--A poll of voters most likely to participate in the Feb. 8 Iowa caucuses found Democrats Richard Gephardt and Michael S. Dukakis in a virtual tie and Republican Sen. Robert Dole of Kansas with a comfortable lead.

The Gallup Poll of 187 Democratic voters most likely to take part in the caucuses showed Rep. Gephardt of Missouri ahead of Massachusetts Gov. Dukakis, 27 percent to 24 percent. The poll, released yesterday, showed Sen. Paul Simon of Illinois with 15 percent, followed by former Sen. Gary Hart of Colorado with 13 percent and former Arizona Gov. Bruce Babbitt and the Rev. Jesse Jackson with 6 percent each. Sen. Albert Gore of Tennessee failed to register significant support, and 9 percent were undecided.

When all 577 Democrats contacted in the telephone poll last weekend were considered, the Missouri congressman's lead widened to 32 percent compared with 19 percent for Dukakis, 15 percent for Simon, 13 percent for Hart and 6 percent for Babbitt and Jackson. Gore again failed to register, while 9 percent were undecided.

Among 154 Republicans who indicated they would most likely take part in the caucuses, Dole led Vice President George Bush 47 percent to 20 percent. Rep. Jack Kemp of New York was third with 11 percent, followed by former television evangelist Pat Robertson's 9 percent, and former Delaware Gov. Pete du Pont's 7 percent. Former Secretary of State Alexander Haig didn't collect enough support to register, while 6 percent were undecided.

Overall, Dole held a 39 percent to 27 percent lead over Bush among 529 Republicans contacted. Kemp was third with 10 percent, followed by Robertson with 8 percent, du Pont 6 percent, Haig 1 percent and 9 percent were undecided.

The poll commissioned by WEEIAM, WCVB-TV and The Boston Globe had error margins of plus or minus 9 percent regarding the Democrats and Republicans most likely to attend the caucuses and of plus or minus 5 percent for the overall Democrat and Republicans samples.