President Reagan agreed yesterday to establish a joint government-industry-labor advisory committee to look into ways of boosting the sagging fortune's of America's steel industry, members of the Congressional Steel Caucus said after a half-hour meeting with the president.

The new panel will be headed by Commerce Secretary Malcolm Baldrige. Steel caucus members said the president did not reveal the other members.

"We're delighted," said Sen. John Heinz (R-Pa.). "It will be of substantial long-term benefit to the steel industry," added Sen. Jennings Randolph (D-W.Va.).

Heinz said the commission would focus on developing joint ventures in steel technology research and development, retraining of steelworkers thrown off the job and "formulating better means of combating unfair foreign competition." But the president appeared firmly against negotiating restraints on steel imports from Japan, caucus members said.

The new panel appears almost identical to the Carter administration's Steel Tripartite Commission, which the Reagan White House allowed to expire.

It is unclear why the president decided to see the steel caucus yesterday, two years after its members first requested the meeting, although there have been a number of Cabinet-level meetings since April on steel industry problems. The industry is operating at a loss and there is massive unemployment with mills operating at 53.6 percent of capacity during the first half of this year.

Rep. Joe Gaydos (D-Pa.), another member of the steel caucus, said Reagan promised to look into the possibility of easing antitrust laws to allow steel company mergers.