HOUSTON, FEB. 28 -- Four of the six Democratic presidential candidates struggled through a debate here today in which the major issues were the absence of the two front-runners in the Democratic presidential race and the value of the proliferating number of debates themselves.

Rep. Richard A. Gephardt of Missouri and Massachusetts Gov. Michael S. Dukakis skipped the 90-minute debate after appearing in one in Atlanta on Saturday, with another scheduled at Williamsburg, Va., on Monday.

The four participants -- Sen. Albert Gore Jr. of Tennessee, former Colorado senator Gary Hart, Jesse L. Jackson and Sen. Paul Simon of Illinois -- reminded their audience of the absentees and then fell into a debate about the usefulness of the exceptionally large number of debates this year.

After the debate, Gore charged that Gephardt and Dukakis "chose to turn their backs on Texas." Hart referred to "the two absent candidates who apparently don't care that much about Texas and the South."

As in previous debates, Jackson played the peacemaker and said the front-runners' absence "does not reflect upon their lack of interest or integrity . . . . They simply had other priorities."

The debate, sponsored by the National Association of Television Program Executives, who held their convention here, and the Sun Broadcast Association of Houston, was clouded from the start by uncertainty as to who would participate. Until a few minutes before it began, there were rumors that only Gore and Jackson would show up for it and there was a report that Dukakis would participate by satellite.

The candidates were frequently halted in midsentence by commercial breaks, and several times their exchanges devolved into an unintelligible squabbling under the free-form format of the second half of the debate.

In addition to the value of the debates, the candidates concentrated on issues important to this area -- a national energy policy, including an oil import fee, aid to the Nicaragua contras and whether English should be the official language of Texas, a matter that is a referendum issue here.

Gore promised to convene a national energy summit conference of the sort suggested by Sen. Lloyd Bentsen (D-Tex.) and reiterated his support for the Democratic plan for humanitarian aid to the contras.

He said there is "a case for a reasonable small amount of nonmilitary aid with restrictions . . . so that it is not used to continue the war effort in order to move the negotiations along."

Simon retorted that Democrats had been fooled by this policy before and said "the last time we voted so-called humanitarian aid, $9 million went for hand grenades." Simon, Hart and Jackson urged emphasis on economic, educational and medical aid programs for Nicaragua.

"These are issues of substance," Jackson said. "The agony for me . . . is that we are trapped in these 90-second sound bites, trying to say something of substance."

Gore disagreed, however.

"Candidates used to sit on their front porches and talk only to those who made the pilgrimage," he said. "I'm for more debates. With technology we can communicate simultaneously with millions on the issues of the day."