The Federal Election Commissino tentatively approved yesterday a legal opinion severely restricting the activites for which prospective presidential candidates may use money raised through special political action commmittes (PACs).

The proposed opinion, which must be approved by at least four of the six FEC members next week, appears to affect Vice President Bush, Reps. Richard A. Gephardt (D-Mo.) and Jack Kemp (R-N.Y.) and Senate Majority Leader Robert J. Dole (R-Kan.).

Under the opinion, issued in repsonse to a request by former Seante majoriy leader Hward H. Baker Jr. (R-Tenn.), prospective presidential candidates would be barred from using "multicandidate PACS" to pay for travel, hospitality suites, aides' salaries and many other expenses if the expenditures are associated wiht active consideration of a presidential bid.

After the FEC meeting, James Cannon, an aide supporting Baker's prospective presidential campaign said: "This means you can't use a PAC to finance a presidential campaign."

Specifically prohibited, according to Cannon, are use of PAC funds to pay for full-time staff assigned to key 1988 presidential primary or caucus states for steering committees and for travel to discuss possible entry in a race. CAnnon's remarks were implicitly directed toward Bush.

Jan Baran, lawyer for Bush's Fund for America's Future PAC, disputed Cannon's interpretation of the opinion.