Tentative agreement was reached Thursday on Sept. 25 as the date for the first of two presidential campaign debates between Democrat Michael Dukakis and Republican George Bush. While top aides were working out details, the rival candidates were emphasizing defense policy during appearances in Texas and Kentucky.

Dukakis told the American Legion that "a mountain of debt" built up during the Reagan administration was endangering national defense, while Bush, observing the fiery destruction of U.S. missiles to comply with a new treaty, hailed "the day we began to reverse the arms race."The tentative debate agreement was announced by Dukakis campaign chairman Paul Brountas who said the two candidates would meet on Sept. 25 at Wake Forest University in Winston-Salem, N.C. Brountas said the second presidential debate would be Oct. 13 or 14 - depending on the baseball playoff schedule.

The debates will be general in topic rather than having one on domestic and one on foreign and defense policy, said Mark Goodin, a Bush campaign spokesman. He said the second presidential debate would be held somewhere on the West Coast.

Vice presidential nominees Lloyd Bentsen and Dan Quayle will debate during the first week in October.

"We are still discussing format, staging and the length of the debates and we will continue to carry on those discussions," Brountas said after meeting with Bush's campaign chairman James A. Baker III.

NBC News president Michael Gartner announced the network would not televise the first debate live because of its commitment to Olympic Games coverage. He said NBC would air a delayed tape of the debate after its Olympic broadcast.

Bush was at Longhorn Army Ammunition plant in Karnack, Texas, to join other U.S. and Soviet officials in witnessing the demolition of two Pershing missile engines.

Sheila Tate, Bush's campaign spokesman, said the vice president now favors an increase in the minimum wage, which has been $3.35 an hour for the past eight years. In line with Reagan administration policy, Bush has opposed an increase in the past.

Tate did not say how much of an increase Bush would favor. Dukakis has made a call for a higher minimum wage a central theme of his campaign.

The nation's largest teachers' union announced its endorsement of Dukakis for president and called for an end to "eight years of teacher bashing," under the Reagan administration.

A new poll, done by Louis Harris & Associates for Business Week Magazine, said Bush had a 50 percent to 44 percent lead over Dukakis among likely voters. The survey of 1,299 people was taken Sept. 1 through Sept. 6 and had a margin of error of 3 percentage points.