In his weekly radio address, Mr. Clinton ticked off economic successes of his seven-year administration and said the course he charted "is the right path for America."
"We can't retreat from this opportunity of a lifetime to keep our economy strong and move our country forward," Mr. Clinton said.
Mr. Clinton vetoed the legislation before his morning round of golf on the Massachusetts resort island of Martha's Vineyard, where the first family is vacationing this weekend.
Mr. Clinton's veto of the $292 billion, 10-year tax cut is no surprise. He promised to kill the measure even before the Senate gave final congressional approval to the legislation on July 21.
"On Capitol Hill, the Republican majority has passed a series of expensive tax breaks to drain nearly a trillion dollars from the projected surplus," in federal budget coffers, Mr. Clinton said in the radio address.
He contrasted his own proposal for smaller tax cuts with the GOP package.
"I support tax cuts, but tax cuts we can afford. We can't afford a $2 trillion U-turn on the path of fiscal discipline and economic progress," Mr. Clinton said.
Rep. Tom DeLay of Texas, the third-ranking Republican in the House, has said that the House's "first order of business" upon returning from its summer recess in early September would be trying to override the veto Republicans had anticipated.
The veto, which comes between the two political parties' national nominating conventions, is tricky for Democrats.
Many Republicans believe Mr. Clinton's veto gives them a winning political issue by demonstrating that with a GOP-controlled Congress, a Democratic president is the only obstacle to sweeping tax reductions.
At a campaign rally Friday in Akron, Ohio, GOP presidential nominee George W. Bush ridiculed Mr. Clinton's decision to veto the bill. "What kind of a tax code is it that discourages marriage?" he said.
On Friday night, Mr. Clinton kept his own tone light at a fund-raising dinner on the neighboring resort island of Nantucket. As he has done frequently of late, he got a laugh when he compared GOP tax cuts to a sweepstakes letter that says "you may have won $10 million."
"Anyone who went out the next day and spent the $10 million ought to vote for them," Mr. Clinton said. "If you didn't, you better stick with us."
Mr. Clinton and Gore call the GOP tax cut plan irresponsible because, they claim, it would spend all the projected budget surplus over the coming decade. Some of that money may not turn up, Mr. Clinton says.
Republicans got some help from Democrats in passing the marriage tax cut package. The marriage penalty is the popular name for the extra taxes 25 millin couples must pay because of a structural quirk in the tax code.
But the bill would also cut taxes for about as many additional couples who now enjoy a marriage "bonus," paying less than they would if they were single. This largely affects families in which one spouse earns most of the family income.
Most of the bill's tax reductions come from enlarging the bottom 15 percent tax bracket and increasing the standard tax deduction for couples filing jointly.
Republicans argued that the measure would benefit millions of middle-class Americans while using just a small portion of the projected $2.2 trillion, 10-year federal surplus. The figure excludes even larger projected Social Security surpluses.
The bill passed both the Senate and House last month by less than the two-thirds majorities needed to override a presidential veto.