Congress Watch, a public-interest watchdog group, is questioning Massachusetts Gov. Michael S. Dukakis' use of two corporate jets owned by Massachusetts companies for political trips in his quest for the Democratic presidential nomination.

He paid only per-person fees instead of a full charter fee. While such use is legal under federal election laws, it amounts to accepting substantial campaign contributions from the businesses, the group said. Direct corporate contributions are illegal.

Last week it was reported that Senate Minority Leader Robert J. Dole (R-Kan.) used corporate jets in some of his presidential campaign trips.

Dukakis spokesman Steve Akey said the Dukakis campaign's use of corporate planes is rare and that it prefers to fly commercial -- and coach: "It's less expensive."

A week earlier, Dukakis had a little explaining to do about a $1 million family trust established by his father's will in 1974. Until a year ago, the trust included stock in companies that do business in South Africa. But in 1983 Dukakis signed legislation to divest Massachusetts pension funds of stock in companies with South African ties.

Why the three-year lag on the trust? Dukakis, who has a reputation for paying great attention to detail, said that although he had been a cotrustee, he had not played an active role in the trust's administration, adding that although he received investment reports, he had not realized that the trust held stock in firms doing business in South Africa.

Akey said that once Dukakis looked at the investments last year, he recommended that those stocks be sold.